The problem with X2 is essentially the same one that plagued X-Men: too many characters, resulting in too little screen time for each one. X2 may be the most ambitious superhero motion picture to date, but it doesn't work quite as well as Spider-Man or Superman, both of which are, in some ways, inferior. The reason is simple: in those movies, we get into the skin of the protagonist, whether it's nerdy Peter Parker or bumbling Clark Kent. In X-Men and its sequel, there are simply too many heroes running around. Unless you're a fan of the comic book series, you need a cheat sheet to keep them all straight – and that doesn't count the cameos (Colossus, Kitty Pride, Jubilee, etc.).
See movie-reviews for full review.