This is a Kingdom Hearts game, so its good. but don't expect anything out of the ordinary, because you've seen it before
Let me start out with the good. The story/visuals are great. The in game graphics are very nice, while the CG cut scenes look great for a DS game. Now the story is probably one of the best parts of the game. This game doesn't really tell a new story, but it gives you a better insight to a sub story of the Organization XIII which ultimately plays a major role in the Kingdom Hearts universe. I wont spoil anything, but the story telling is great and it really sucks you in and it's one of the best.
The gameplay is also nicely executed. It is fairly similar to the other Kingdom hearts games, but it is slighlty adjusted for this game. In the menu screen you have a panel that has multiple slots on it. And a new slot will open up everytime you complete a mission. In these slots you can put a weapon, spells, level up slots, and other items. But you have a limitednumber of slots. So for example if you had 6 slots open you could put your weapon, a few spells, a few items and a level up slot. And if you have two slots for spells then you only have two times to use those spells (unless you use an ether). So its all about customizing your panel to make things work for a particular boss/manager. This is a nice new addition to the series, but again the actual gameply mechanics aren't that different overall.
The game is played using missions. It doesn't really have a main mission. You travel to all the similar disney worlds you've seen before (agrabah, Halloweentown, twilight town, etc.) and you just complete different missions like: defeating a boss, collecting certain items, or defeating a certain amount of enemies. Then after beating a number of missions the story continues to unfold and you learn more about the Organization. I wasn't a big fan of the mission style gameplay but it wasn't horrible or anything.
The music is all recycled from the previous games excpet for one or two songs which arent really worth mentioning. Also besides new bosses, all the enemies you fight are ALL recycled from the first two games. This isn't the worst thing in a game, but all these things add up and eventually make the game less appealing.
Overall, this game is good, don't get me wrong. Just don't go in expecting a whole new Kingdom Hearts game. It's very similar to the other games, which is good but not $35 more. If you are hesitant maybe rent it first or just play through the first two kingdom hearts again. If you're a fan of the series like me, you'll get enough enjoyment out of it. The story is worth it and playing through similar environments and fighting similar enemies won't be so annoying after awhile.