Meh, it does what it was supposed to, I guess.
Kingdom Hearts:Chain of Memories is the bridge between KH and KH2. Sora and the gang find themselves in a castle created from Sora's memories. Each floor is a stage (most of the time) from KH and Sora must travel these stages to regain his memories, which dwindle as he travels up each floor. Inside, he and the others lost all their abilities as well and pretty much have to start from scratch. However, the only way to battle through the enemies is via a card based real time battle system.
The fact is, the game, (I don't think) was intended for anything great in the first place. The way they ended KH, they pretty must HAD to have a some sort of bride to make KH2's story make sense. That is what this game does and, yeah, it does a good job at it, but in terms of a game, its extremely mediocre.
The levels are more or less all of the same without any variation. You go through about 5-6 rooms in each stage, listening to Midi versions of the same tunes, take down heartless using the sometimes awkward card system, get key cards to open doors, make your way to the boss, boom- next floor. Rinse and repeat. And to make things even more mediocre, much of the story in each stage is pretty much the same from KH. The only real enjoyment story-wise is when your in the actual castle and you encounter your new enemies, the organization. That's, honestly, all this game is even good for.
As strange and annoying as the card system is.. it can be fun and challenging at times. I had a blast fighting certain boss battles (Hades was a b****) and configuring your deck to your liking throws in some strategy aspects. But ultimately, when compared to the rest of the game, it's just a shell of the real battle system from the other games.
Now, don't get me wrong, this game is worth playing. It has it's moments. The graphics are actually quite impressive for a GBA game and plus, it's a Kingdom Hearts game. If your a fan, then go for it. I'm just warning you, it gets boring and you more or less have to push yourself to get to the interesting and fun parts. Especially to get to Riku's side of the story, which, in my opinion, was better than the regular story =P