The game has some great features and is an amazing addition to the kingdom hearts series.
The story...
Basically, it leaves off from the first game, where Sora, Goofy, and Donald sealed kingdom hearts and chased Pluto down a winding field because he had a letter from king mickey in his mouth. They ended up at Castle Oblivion and went inside. There, as they advance further into the castle, their memories seem to slowly dissapear......
Combat...
Using cards, you either attack with A, using single cards, or pressing L and R together to stock 3 cards and unleash a combo. There are maybe 10 types of attack cards you can use with different power levels, 6 types of magic cards, and 7 types of item cards. You touch an enemy and you go against a few heartless and begin to fight.
Leveling up...
You can level up either Hp(health), Cp(card points: the number of cards in your deck increases), or occasionally a new sleight(a special move by putting certain cards together).
Graphics...
For a gameboy game, the graphics are actually really crisp and clean. Camera angles are very wide, allowing to see almost everything.
Map...
In each world you visit are doors that lead to other parts of that world. After fighting enemies you get map cards with different values that open the various doors. All the cards have different effects so try them all out if you can.
Story(continued)...
The cool thing about this game is that you can play as Sora or Riku! I've gotten both up to level 99 so they both rule. The stories are well told and keep you interested until the very end. Each story ties in to the other but in a different way.....
Overall...
I always thought Kingdom Hearts was cool, but I didn't have a PS2. So I got this one. I am really glad I did! Everything is great about this game except maybe for the music that gets kind of repetitive and some difficulty with cards(not anymore but for others), but other than that this game is top notch!