90s start slowly, but accelerate rapidly in releases, so can't observe decade as a whole. The winner by default is the only partially translated title Sekai de Ichiban Kimi ga Suki (1990).
Takeda Shingen (1988) made a great impression on me while Tokugawa Ieyasu (1983) felt like a firm masterpiece that filled quite some blanks for me. I think I'll just rate everything not translated as 6 for convenience purposes and inability to evaluate, won't comment on those for the same reason except first few when I tried to squeeze smth.
Mydramalist has thousands of doramas, so I exclude all those I can't find or equal/under 30 minutes length or under 3 episodes long or belonging to Detective or Wuxia or Sports or Boys Love, or sequels (unless only sequel gets subs), maybe some more blacklisted categories to follow. As expected, found almost nothing from the 60s and not much from 70s. Among the subbed ones only consider Ogon no Hibi (1978) a masterpiece.