It's kinda the same when you look at the other DOS games, despite rough last Acts (How rough on release, idk exactly), and they're in the high 80-90s. Hey, I understand that too, I use to think DOS2 was the best RPG around, but after finishing it (and replaying Act 1 -> 2 probably too many times), that opinion descended quite quickly to the point that I just cannot touch it ever again.
Well I guess this depends on the methods used in critical evaluation. Some break down the game into systems and evaluate them separately, i.e. gameplay is a 10, story is 8, graphics 7 etc. This seems like a universal and just approach to evaluation, but I find it deceptive in terms of representing the game's true value. If overall enjoyment the game brings is immense, it would not be just to extract some points just to check some boxes on the evaluation sheet. There should be phenomena and exceptions, when a game gets high scores despite its technical flaws or other mistakes, just for the sake of being a wonderful experience overall.