This is such a difficult thread, because such sequels are usually something we don't really want to remember. Anyway.
Crysis. I don't remember everything that made the second game bad, but I'm thinking it was the (too) distinct setting, removed freedom, poor enemy AI, and animations during which enemies were (or at least seemed) invulnerable (mainly ladders, I think). I'm more interested in the third game than in the second, but after the terrible second game, I still haven't actually wanted to try the third one enough.
Final Fantasy X-2 was also just mentioned, and I couldn't agree more. I can forgive a lot about the game, but the changes to the characters were simply poorly written, and besides the main hook of the story, the story was a huge letdown if I recall correctly.







