IMO, KH 1 is better than KH 2 if only for replay value in terms of having more places to visit, more secrets to unlock and basically more moves and variants of limit breaks to unlock. Plus, although the story is simple, it is still deep and complex enough of a plot for those who care to look deeper into it although marketed as a kids game more so than say the Final Fantasy games.
KH 2 was such a disappointment in a way because it sort of failed to deliver a good solid game like part one, and a lot of it was bordering on tedious as Sora was not even in it for the first half basically and not many people liked Roxas or Namine as, at least with the first release before the extended cut was released aka KH 2 Final Mix, and so many wrote it off. Graphically it was great, but to me came off as too linear and easier than the first game. Honestly, I thought they rushed some parts and over stayed their welcome in others and it still boggles my mind that part two took nearly four years to complete and the end product felt so bare bones by the end of it.