I think KH2 really improved on the controls, loved that, always had a hard time with it for some reason.
Anyway, I like all the extra bits they added since the originals, extra bosses, more areas, some things like that are always nice to add. Gives you something to shoot for.
I remember in KH2 that I really wanted to 100% the game, one of the only games I really wanted to try that with. So there I was over 40 hours of solid gameplay, checked the lists of things that needed doing, and found out I missed only a single treasure...in the start of the game you can't go back to...soooo miffed at myself for doing that >.<