For me the best VN of September 1999 is Kazeoto, Chirin. There's such well known game as Memories Off as well, but a I place a good midscrew over a good slice of life in most of cases.
1. Love Lesson ラブレッスン  Melody
When our guy ask a girl to be his steady, he found out that she loves someone else. While drunk from depression, he made a mess of helping his new neighbor. It turned out that his new neighbor is his new homeroom teacher. What fun, now he can chase after his teacher or the girl that rejected him.
There is one pure love and an one insult route. The romantic route is quite thorough, but the picture quality is rough.
2. Tomoyo Venture Episode1 知世べんちゃー Episode1  Atelier Kurimami
Main character comes to Chi-chan's house to play. It all starts with laughing and cuddling, but can take young people far.
Doujin H-tilt crap
3. Escape ~Akizora no Roof Garden~ エスケープ ～秋空のルーフガーデン～  Telluru
October, before the school festival. Main character painfully recovers from his lover's death. At school rooftop he decides to move on and pay attention to school girls.
Genre is sentimental novel. Basically it's chasing school girls at the pauses between lessons and at free time. Guess just sentiments and rooftop is not enough for auditory already - game got zero reviews.
4. Fushidara Fu・shi・da・ra  Mink
Our girl is one of those people who can't even think of H stuff. When she start to have exciting thoughts about her boyfriend(our guy), she has to seek counselling. What she got were some tapes and a bottle of perfume. While watching the tapes and inhaling a drop or two of that perfume, she has fun dreams with her boyfriend, guided by one of her friends. After a few sessions, she just might gain enough experience to live a happy life with our guy.
There are three girls apart of main heroine. Most of H events are happening only on the tape. But the reality H events are interactive touch ones. Length is insufficient.
5. L L-エル-  TopCat
The story takes place in the two weeks right after the protagonist graduates from university.
There's nothing to add to the synopsis. The guy studied so hard that he never seen the city he was studying at and only after graduation went breaking bad. There are eight characters overall. Capturing one heroine takes some hour while not accustomed to the system and some 20 minutes afterwards, so there is a feeling that the content is thin.
6. Be-reave Primary Be-reave Primary  Unison Shift 1
A collection of short unrelated H-AVG stories, each drawn by different artists. You start out with 3 stories to choose from. More stories may be unlocked as you complete the stories first available to you. Though the length of each story is pretty short, there are many crossroads to be made that do have an impact on the flow of the story, unlocking various events and scenes and perhaps even multiple endings. There is more to each story than meets the eye. After you complete each story, a green bar will show how much of that story you have covered, giving you an indicator of something you may have missed.
There is an English review.
7. Be-reave Secondary Be-reave Secondary  Unison Shift
There are four mini games in this part. In Blueeyes/graymaN, a guy got his wish of seeing a girl he met long ago, but might have some trouble keeping her. In Sora, a terminally ill guy might get saved by someone who love him. In Instant Spir, a guy can help out some special people. In Gyu, with two magical girl's help, a girl can't go wrong, or can she? Again, there are extra endings if you played all four mini games, but you might need to get the bug fix file to see them.
The structure is the same as first game, so can generally refer to that game review.
8. Five Card ファイブカード  Cross Net
Main character is a new teacher in a private high school. There are five girls that stand out among the class and rival for teacher's attention. Will new teacher be able to do a good job in such circumstances. What is the mysterious prostitution organization dwelling in the shadows of the school?
All the choices have two variants with one variant usually being H-scene and game over and the second moving forward, so basically it's a one-road scenario. Graphics are really cute and form the main appeal point. But in the end it's just a nukige, that's why there is a hentai anime of it as well.
9. Inda 2 淫打2  Hyperspace
The second bullet in erotic keyboard lessons with strengthened erotic aspect. This time successes and failures are not only accompanied by voice, but by animation as well.
Native English speakers read English sentences, so it's a good way to brush up English skills.
Animation during typing is poor with several paranoid pieces cycled. Text drawing is too slow and can't be adjusted. Content is really low quality, even in H sequences.
10. Kairai no Hazukashime o Kimi ni 傀儡の辱めを君に  Fuuro
Hero is given the power to manipulate girls after meeting girl Sarah. It's not a complete control power, so needs to be mastered on daily basis.
Multiple branch scenario. There are other girls but Sarah as well. But do you really expect an interesting story from the game that has "humiliation puppet" in the title?
11. Kazeoto, Chirin かぜおと、ちりん  C's Ware 1
Satoshi, the protagonist, and Takashi his best friend, are both college students who came back to their old town to spend their summer vacation. In their village, Satoshi came back to his small house that is now an inn since his mother died.
But there was some event going on there.
"People will disappear" - a strange woman says to him.
Residents suddenly start to disappear without any reason.
The most optimistics came with the opinion that many people are being spirited away. And no one can avoid that. The hero decide to look into the matter.
"Do not try to solve this case without us" - said his friend Takashi to the half-hearted hero.
I've actually already written a full review of this work
12. Megami no Haka 女神の破瓜  Speed
Goddess of Salvation is spreading chaos, devastation, conspiracy, rebellion in the fantasy world and it's not clear whether it's for destruction or creation. Carmine controlled by the spirit of the goddess is looking for a shrine maiden holding "the beads of gods".
The player takes role of an inquisition officer who aims to eradicate the rebellion spreading around the country and to suppress those who receive the trust of the heretic Goddess of Salvation.
Game's is noticeable for a heavy dark fantasy atmosphere. There's quite a lot of infodumping. In the first half main character moves the story but later on he just moves with the flow. There is no good ending. It may be quite close to being an eroge, but it's impossible to know since the game's is very rare.
13. Smile for Me  [K]rimzon Fake
Main character suddenly becomes an adventurer. But he does not know any magic or how to use a sword. But there are so many pretty girls around to drag about - he needs to try his best!
There are 8 girls with different personalities and strategies. Game is mostly about collecting items and that triggers new events.
14. Sweet Palace  Zero
Hero got a job as summer hotel manager. The staff and guests will keep him busy!
We need to choose locations and meet girls/trigger events. Graphics are rough. It's all packed with H events through and through.
15. Tokyo Nyoshuu Shuukanjo 東京女囚収監所  M'
Main character is a man of great wealth and power. His new quirk is taking prisoners and training them as slaves.
There are five prisoners to train. Depending on the means of training there are different endings.
16. V.G. Max  Giga 1
A game in which the V.G. waitresses are rendered as super deformed (chibi) style characters. Includes the original six V.G. contestants, as well as Satomi Yajima from Advanced V.G., Tamao Mitsurugi from Advanced V.G. 2, Yumiko Watanuki from V.G. II and new character Masako Houjouin.
It's the franchise that comes from the pre-windows era and it's at least the third title in the V.G. fighting series (not visual novel fighting, but real fighting fighting), but it must the first one with substantial ADV part. It's the first such mix with very active fighting action gameplay. There are H insult scenes present. V.G. MAX is said to be of better quality than the predecessors and holding a new interesting character, but overall a very average passable game.
17. Zetsubou ~Aoi Kajitsu no Sanka~ 絶望 ～青い果実の散花～  Studio Mebius 1
A guy got killed because of what he did. Since he still wants more, he is back as a ghost to get some. His servant(ghosts too) found him a place and a brain dead guy that he can take control to get more girls. As for how many more, how about 28 girls total, plus some side shows. This time, he can even take over a girl's life or do whatever he likes.
There is an English review.
18. Tokyo Mermaid TOKYO魔迷奴  Ryuujinsha
Tokyo survived a massive earthquake, and the ruins of it turned into an illegal zone.
Langhao and her sister Mika, a cosplay masochistic young lady, encounter a mysterious cat girl creature. The three people start to travel together and notice the shadow of a mysterious organization. Nonstop erotic survival battle develops in Tokyo set into ruins. What is the true identity of a cat girl? And what is the conspiracy behind the mysterious organization?
So you think game's crazy already? The reality is even more severe. Add to that the fact that it's possible to save only at the end of each chapter, poor graphics and very poor voicing. There's no thing as description in the game - only dialogues and often even in form of manga strips to add action. The story is crazy by itself.
19. Kimi no Kimochi, Boku no Kokoro 君の気持ち、僕のこころ  Takara
Main hero is a high school student adept in sorcery. He's got the power to possess other people & even animals bodies.
You don't really possess others as you can't control them - you just peep from their eyes. There are three main heroines, but you can haunt pretty much anyone at any time, so it's very tiresome to try out all the combinations and see if it works. There was no manual released at that time so it was a game of guesses. Difficulty is skyhigh because of that. There are also some technical questions like a very long load time. Heroines aren't attractive enough and it's not clear what's the target auditory of the game.
20. Eve Haze ~Biyaku no Ou-sama~ ｅｖｅ ｈａｚｅ～媚薬の王様～  Brownie
A plague fell upon a village killing most of inhabitants including both pharmacists. Only the son of pharmacists Diano survived. He found an old book about aphrodisiacs and started his study. At the same time something strange happened to monsters of this country...
Hero needs to prepare recipes to solve individual troubles or make monster bosses surrender. The main part of the game is collecting different herbs on a map and brewing potions which does not make it much different from Little Witch series. What's different here is card battles with the monster bosses.
21. Joousama to Oyobi! 女王様とお呼び！  Side-B
Main character is a devil king. He has lots of servants from different races. One day he is brought a noble human girl. The devil king is going to make her a queen. For that she must undergo a thorough training.
A training SIM with fantasy entourage as the only prominent feature. There aren't any reviews to peek at end content around.
22. Paradise ee  Hyperspace
Main character is a member of resort club and is sent to a remote island called paradise ee. There are four angels working here as guides during day time and giving private service during night time.
Game itself ends in less than an hour. Picture is rough and backgrounds are very extorted.
23. Saikidou ~Shiawase na Ashita no Mukaekata~ 彩季憧 ～幸せな明日の迎え方～  iMAGE CLUB
Main character lives alone and prepares for entrance exams to the university. One day he dies by accident. Just before his death he regrets about not having fun during school years, and a miracle happens - he gets resurrected from the second year in high school. This time he's going to have a happy school time!
You need to choose a club to attend. Each club corresponds to one girl, each having an ending. Drawing is rough and rendered real time photos are mostly used as backgrounds.
24. With You Toybox うぃずゆーTOYBOX  1 2
This is a side-item to With You with lots of wallpaper and mini games inside. Mini-games include:
W-Sisters CD Player
Naori no Hyper Udon
Manami-chan no NekoNeko Panic
EBC News Scramble Special Edition
Mini Adventure/Side Stories
Haneru! Keiji Gotouda - The Worst 3 Days in the History of S.P.S
The Legendary Archangels - Card Survivor
There is an English review.
25. Court no Naka no Tenshi-tachi コートの中の天使達  Pinpai
Two sisters manage to get our guy out of his depression of pass glories to train his team of girl volleyball. In mode 1, he has no choice but to use the girls for revenge against the volleyball league. But in mode 2, if he can complete mode 1, he can find a girl to love.
Basically it's a raising SIM training several people at the same time for three months. Best use walkthrough since consequences of choices aren't evident in the short run but may already doom your team without your knowing.
27. Little Witch Reinette ~Swan no Namida Rhapsody~ リトル・ウィッチ レネット 〜スワンの涙ラプソディ〜 
It starts with a magical competition mentioned in original Little Witch Parfait. Now from Reinette point of view.
It's been just five months since releasing the original. So, did you even wanted to be a magical girl and create wondrous recipes? Well, I did not.
28. Maboroshi Tsukiyo まぼろし月夜 
The player takes the role of Takashi Tanaka who one summer night meets a ghost of a girl in the park, and this ghost starts living with him in his apartment. The ghost can enter other people's bodies too...
Usual trigger events on the map system. The period is two months. The appeal point of the game is the background of the ghost heroine. She died in Taisho era and is a typical Yamato Nadeshiko. There's a huge culture gap that's the scene for many jokes. There are a lot of colorful characters who are interested in this ghost for various reasons. You can easily shift to one of them, but you need to exorcise Ayame spirit for that, then it's an ordinary galge. But if you pursue Ayame, there's more of the story and as many as two endings prepared.
29. Toriaezu Air Plants! とりあえず えあぷらんちゅ!  Air Plants
Fan disk contains short stories on games Dearest Vampire and Fluorite ~Hotaruishi~, demo versions of both games as well as CG, deskop accessory, minigame, music tracks, staff and new works information.
Since it's a fandisc, gg.
30. Album no Naka no Hohoemi アルバムの中の微笑み  Curecube 1
You as male main character returns to japan after completing your Europe ART studies. As a rich man's son you were allowed to travel around to seek education around the globe. Now that you have completed your quest its time to return to japan... and marry Satsuki, your preset bride to be. There is a problem, you have got a maid that's been following you most of your life. She likes you. After arriving in Japan, you soon became the art teacher of an all girls school. Now 3 more girls join the wagon and they all want a piece of you alright. Who would you chose?
There is an English review of this work.
31. Berries ~Kagayaku Kisetsu ga Owaru Mae ni...~ Berries ～輝く季節が終わる前に…～  Pocket
Summer. Yuusuke Sugihara runs with a father a family restaurant "BERRIES". One day Yuusuke wakes up and finds a letter on the desk saying that his father went surfing and that Yuusuke should be store manager in his absence. What kind of memories will he gather by the autumn?
Pocket tried to get into the pocket of gamers and put such high price for this usual setting game - 9,000 yen - that there is still not a single proper review of the game. What's known is that the game has terrible systems, but quite normal content. Still, it' feels more like a doujinshi in a box rather than a professional work.
32. Costume こすちゅ～む  Optim
One day hero helps a strange looking girl. He allows her to change clothes at this home, but as soon as Sarah rose hands to change clothes she was covered in a whirlpool of white light appearing in a nurse suit. Thus, a strange cohabiting with Sarah began. But Sarah's younger sister Kira came to pick her up and made a fuss about it.
A cosplay nukige.
33. EA Mind  LiLiM
Near future. Private Maritime Academy is governed by students and its head is student council which consist only of women. All the male students study in oppression there. Main character deliberately transfers to this school in order to set male dominance there.
Frankly speaking, only first part is about domination since in the second part he chooses one of girls' paths. You move around the map and trigger events and fights. Fighting is led till you embarrass opponent enough winning in hit/block game for five rounds. There are five girls to capture. Atmosphere is light and there are enough funny moments. Game period is 10 days and play time is around 5 hoursg.
34. Entrance ENTRANCE  TinkerBell
Tomoya Kamijo returns to his hometown after 12 years. He has no clear aim and during university course "Learning ways to create a future" he learns his due course.
There are four heroines. All the characters are linked to the psychology department and this game was supposed to be as close to reality as possible, it's written in a manner of a book. That's all that's known and I bet the price of 8,800 yen has played an important role in that. Pretty soon Tinkerbell will drop all those psychology movements and will only be making hardcore eroge.
35. Guardian  Aaru
Our guy woke up in a dungeon without his memory. What will you have him do? Live life unknown, or go to town and find out who he is? This may sound like a role playing game, but it is a pick your choice adventure game with 90 different endings.
Oh well this kind of games again. 90 endings and stories are ultra short (some 5 minutes) and follow some typical pattern. It's enough to entertain, but not for everyone.
36. Kaiki! Drill Otoko no Kyoufu 怪奇！ドリル男の恐怖  Tetratech 1 2 3 4
Three schoolgirls are wandering in the forest, looking for the pension, where they planned to spend the night. However they are stumbling upon a seemingly empty mansion in the middle of the forest instead. Since the sun is about to go down and it's raining anyway, they decide to spend the night there.
However, the Drill Man appears soon after and tries to hunt them down. Will they be able to find out the secret of the mansion? Will they make it out alive? Or will they be captured and kept as playthings for the mysterious inhabitants of the mansion?
Game is localized and has English reviews.
37. LOE ~Legend of Enomoto~  Aaru
Our guy received an invitation to enter a contest to win a very rich man's inheritance. The contest consist of quizs and games. Other contestants will compete with him. He can either do it alone or with someone's help.
Forget about the story here. There is more to the synopsis in here, but the story does not lead anywhere. It's puzzles + H events and since it's reported that the quantity of H-events is ordinary, I'll leave it be for now.
38. Mania na Onna 2 まにあなおんな2  Foster 1
The game is set in modern Tokyo, and is divided on chapters. On the first chapter, you are a college girl and in 5 days you find out why your boyfriend is cheating on you. On the way you pick up a lot of new characters and at the end of that if done right you will have sex with your boyfriend. On each chapter, the protagonist is different but all the characters know each other.
There is an English review.
39. Rapture  Gondola
You start on a floating island, grappling pillars and pushing buttons till the bottom of the cave turns to grass. After that you get to know that your girlfriend is cheating on you. You're going through her memories to get to the bottom of it.
It's almost as if the developers had been playing LSD Dream Emulator making this weird 3D maze with tons of pre-rendered horrible 3D H videos.
40. Snow White ~The Veil of My Heart~  Eden
A small town between the sea and the mountains. The last school year passes by and main hero has time before Christmas to settle his feelings.
Hero suffered from consequences of his parents divorce and only partly recovered from that by the last year of school. There are 8 girls. There's a month of time. Both pure love and devil mode are available for the girls.
41. Tenshi no Wana 天使の罠  MBS Truth
Main character was leading a normal school life till an angel visited him depriving him of virginity. After that things start to change around him - men and women start masturbating and having sex everywhere.
Nothing to see here, just MBS Truth keeps making weird nukige with enormous speed.
42. Tousatsu Mania Act 1 TV Kyoku 盗撮マニア ACT1・テレビ局  Waffle
I want to see... even if I commit a crime...
I want to know more about this child ... her real face that can't be seen on TV...
I want to make private photos of her and to take her belongings...
This is a story of one young man who stepped on an evil path of voyeur.
Nothing good can come out of a game titled "Voyeur mania". The purpose of the game is walk around TV station without being caught by guards, set surveillance equipment and hide in waiting.
43. Waru Gaiden ~Akumu no Rush Hour~ 悪っ外伝 ～悪夢のラッシュアワー～  Interheart 1
The legendary mischief master Honda is released from prison. He thinks of finishing with molesting, but he sees a seducing dancer and goes breaking bad. At the same time the railway company hires two new girl staff memebers - morality countermeasures expert Shinomiya and national idol Hayakawa. Can they pose a challenge to Honda?
An improved version of Waru!! ~Itazura~ with two new characters. There's even an English review.
44. Yuuhei 幽閉  Deep Zone 1
"I will teach you a way to sneak into Women's Dormitory."
One day, such flier get into main character's house. The phone number on it belongs to a girl who lives in the same dormitory. For 30,000 yen she tells all the secrets of this building. As it turns out, hero was chosen not by chance - the fate of all dormitory women greatly depends on his behavior.
I'm very disappointed with previous D'z works and this one is just a nukige as well.
45. Blow ~Michita Tsuki, Kaketa Tsuki~ Blow ～満ちた月、欠けた月～  Rock Climber
Main character is a normal high school student. During the preparation week for the culture festival a series of rapes happens right at the school campus. Who is the culprit? What are his motives? Can you get to the truth?
Basically hero investigates the victim girls, befriends them and can find love with one of them. One of such "good" endings finishes with cannibalism. There's also the True ending. A heavy work of very bad aftertaste, mostly because of how realistic it is.
47. Memories Off メモリーズオフ  KID 1 2 3 4 5 6
It's a surprisingly bittersweet tale about a guy named Tomoya Mikami who actually was dating the girl of his dreams, Ayaka Hizuki, for a long time...only to have her die tragically a good while before the game starts. The game even begins with Tomoya having a flashback about Ayaka whilst walking to the train station to get to school. On the train, as usual, is Yue Imasaka - a close friend of Tomoya and Ayaka who pretty much grew up with them. The gist of the story is that Tomoya feels that he's spent enough time grieving over the loss of Ayaka and is ready to try his hand at love again and hopefully find another wonderful girl to make beautiful memories with.
Game has English reviews.