Amazing storyline, weak battle system. Possible spoilers
My synopsis is no where near as good as the actual storyline, which is the most redeeming thing about this game. Once again, there's a focus on friendship, but an even larger focus on memories, which makes for an amazing story. Another cool thing about the game is that **spoiler** once you beat it as Sora, you can replay it as Riku, but it's not the same. He has his own little plot (which ties in with Sora's somewhat), cool controls, and etc. **end spoiler** That may prove as a large plus to Riku's fans from KH1.
The battle system is a sore point in the game. As I mentioned, the castle is ruled by memories are cards. Memories of Sora's from the first game are used to create (or, rather, recreate) worlds and enemies, which is cool. However, in order to battle, you must scroll through cards bearing different types of keyblades, different magic spells, and summons. It's quite disorientating and aggravating and can seriously turn off a player. After a while, it can be adjusted to, but it is still a major cause for grumbling.
The graphics are neither amazing nor horrible. The sprites and whatnot are cute, and there are a few "cinema" scenes, which are definitely (obviously) no where near as good as the ones in the original game.
I would still suggest this game to any Kingdom Hearts fan or any other gamer as I adore the story line, but the battle system definitely makes or breaks it.