I really wish i could write 2 reviews on this game instead of just one, because the single player and multiplayer are almost like different games, that's why i'll split this review in 2 parts: Single player and multiplayer.
Multiplayer: The main reason this game is so good is the multiplayer mode. In it every player uses his GBA to play, including player 1. This isn't a bad thing like most people like to put it, since you can acces your menu while the other players continue, or have all players visit a different shop at the same time. Also when multiple players use a spell at the same place the spell will fuse and become more powerfull (Fire+Fire=Fira), it's not an important feature but it makes playing a bit more fun.
The stats are upgraded by artifacts wich you can choose after defeating a boss, every player will have a bonus mission on his GBA screen, and the player with the most bonus points will get to choose first.
Single Player: Allot less fun, but still a good game. Sometimes it seems like they haven't even tried to make the single player good, but because this game is almost exactly the same as the multiplayer it's still fun enough to play. Some things do get annoying after a while, like getting another Life spell, or trying to do something that clearly was made for multiple players. The battles have become way too easy because the chalice no longer has to be caried around, a moogle does it for you at all times, even while fighting.
FF:CC fails as a single player game, but easily surpasses most games when it comes to multiplayer.