I've said this multiple times, and probably everyone has heard it already, but here goes again.
I think KH1 sucks. I think KH2 is simply fantastic. The original has one of the worst cameras ever put in a videogame, your party members are idiots and the game controls really badly (come on, was it so difficult to implement camera control with right analog). The story was ok, nothing incredible, but nothing to criticize either, it just got ruined by a very poor gameplay (actually, not gameplay, the idea is great, but the execution was really poor)
Move on to the second, and you have a game that fixes every single flaw of the first. Camera control, at last. This fix alone makes it infinitely better than the first game for me. More intelligent party members, perfect controls. Skippable cutscenes! Plus, they added the drives that are simply amazing. The new more complex story fits the game really well too.
So, in all, KH2 is everything the first should have been, and more, much more
EDIT: And as Mirson said, Gummi Ship in KH1 sucks, Gummi Ship in KH2 is actually fun
