I agree that Kingdom Hearts' difficulty was the best in terms of actually feeling like the Heartless actually posed a threat to you, or Sora, even at a higher level. Kingdom Hearts II Final Mix' critical mode was difficult throughout the whole game, especially the added on content. I found critical mode to be hardest in terms of bosses, but proud mode on Kingdom Hearts was the most difficult considering the gameplay in general. I'm not sure if either of you have played Kingdom Hearts II Final Mix so I guess just take my word for it until 2.5HD comes out. It is kind of ridiculous how much is fixed in the Final Mix versions of the games, though.
