We got Son a number of games for Christmas, and Kingdom Hearts is the one he was least certain he wanted, but the one he's been playing the most. Every afternoon when I come home from work, I get the daily 10-15 minute KH recap, like it or not.
On the whole, I like KH, but not nearly as much as Son (although it'd be hard for me to like any game as much as he likes KH). It's actually an interesting game, but more because of the introduction and storyline than the gameplay. The intro made me think it'd be quite a deep game; playing it has left me a bit confused at times, as it's not as clear in KH which way to go or what to do as it is in other games (I'm thinking of the Spyro games, although those are sort of in another genre).
And that's an interesting thing in itself. Used to be that on the one hand you had arcade games, and on the other, role-playing games. Moving into the 3D world has blurred the distinction; in both, you play a character, and in both, you can do more as you solve more puzzles or challenges. The main distinction left is that of increasing levels and hit points, and the number of tools, weapons and toys available in RPGs.
Anyway, it's a good game, and at Son's insistence, I'll continue to play, although at present I'm more interested in Jak and Daxter and/or GT3.