One of the few movie sequels that I have to like better than the first is X2: X-Men United.
Why? One of the reasons is because we get to see John Allerdyce, aka: Pyro, (played by actor Aaron Stanford) in the movie although I do wish they had added more background detail to his past. Another reason is because there was a lot more action. Or at least to me it felt like there was more action put into it.
Also liked Star Wars, Episode V: the Empire Strikes Back and the Lord of the Rings: the Two Towers. :)