I'm a massive Sonic fan, and this game was no dissapointment. The plot is interesting, the chacters are varied and fun to play, and the graphics are excellent.
But it did have some bad points - for one, it's all battling or moving (by moving a cursor around te screen) to different areas so you can get to a battle. It gets boring easily, and often you'll have battles straight after another.
The opponent A.I. level is constantly changing, making some battles difficult.
Emerl, with her changable attacks, is an interesting character. She fun to customize, but this can lead to frustration when you battle the one character 20 times and don't et the card you need. I ended up using a gameshark out of frustration, which really spoiled the game.
Another interesting character was Cream - in most of the battles where she's your partner, she doesn't fight. It's interesting, having a pacifist for a battle partner.
Another thing that bugs me is the ending. Basically, when you're finished, you're treated to some great scenes which I won't spoil, then Tails appears then says fighting is bad. At the end of a battle game. Not only does it sound lame, but it goes against the whole game!
Basically, this was a great game, and despite some niggling problems, it enjoyed it. Even after the main game is completed, there special battles and mini games (the best ones are multiplaer, unfortunatly). It's well worth getting!