Kingdom Hearts 1&2 were solid action RPGs whose main flaws were the lack of difficulty and the narative. The pacing was generally pretty good though the grinding to deal with the side content, at least in the first game, was pretty obnoxious, as grinding always is. The gameplay was pretty rewarding: combat was engaging, despite it's ease; the level design was good, providing interesting terrain to fight in, solid platforming, and good aesthetics.
The reaction commands in KH2 were a good idea but, as previously stated, lacked polish and created too many "Press triangle to win" situations rather than "Press triangle to have new options". How it should have been done, I don't know, but what was there didn't quite work. All in all, I'm very interested in FFXIII Versus because of them.