Everyone needs to play this game, but....
The problem was, I needed to play this game if I ever wanted to get the full story of what happened in between Kingdom Hearts 1 and 2. So I gave it a try again just recently (2 years later) and made myself relearn the card battle system, and I made myself like it enough to get through the game.
All in all though, I felt this game was lacking. I do need to make clear that this is the first "side game" in the Kingdom Hearts series that I've played, so I realize it's not going to be this huge awesome story like the main titles are. The story itself was satisfying, and more than filled in that blank in my mind of what happened between the first two main games. That is, when you actually were allowed to experience the story.
Eighty five percent of the game is you traveling through these rooms that mirror previous worlds that were visited in Kingdom Hearts. The only time you get to experience the storyline is in between those worlds where you'll get a brief scene involving Sora, Donald, & Goofy slowly losing their memories as they progress through Castle Oblivion, or clashing with various Organization XIII members as they make their way to the top.
I guess I would ask for more story progression in the worlds, as well as in castle oblivion. It would keep things a little more interesting, and not make the world visits feel so pointless. Other than that though, not bad at all! They should make a note at the beginning of Kingdom Hearts 2 though: "If you have not played Chain of Memories yet, please turn this game off now, and continue after you complete Chain of Memories. Otherwise, you will be as confused as a purple sky for about 3 hours into this game before you finally start to grasp what may have happened."
Yep, I'm guilty of doing that. I don't live on game message boards like I used to, so I honestly had no idea. Kingdom Hearts 2 after Kingdom Hearts 1, duh!. And by the time I started realizing "wait a minute, when did this happen? who are these people? what is this!" I was too progressed to really have a mind to quit, so I trudged through. A side game should be a side game, an "extra" storyline so to speak; because as far as my opinion goes now, Chain of Memories should be renamed Kingdom Hearts 2, and Kingdom Hearts 2 should be renamed Kingdom Hearts 3.
I'll give the game a solid score of 6.5/10. The story was great, but the card system took some getting used to, and the worlds were pretty stale feeling. Everyone does need to play this at least once though.