Believe it or not, this game totally rules. Even if you don't go for the whole Sonic vs Mario dreammatch thing, the mini-games are way too much fun, especially with friends. Characters are divided into sets (Speed,, Power, Skill, All-Around) and have 4 characters per category, for 16 characters total. My only real complaint so far is that a lot of the Mario characters have lines recycled from old Mario games. Peach and Daisy retain all their lines from Mario Kart: Double Dash!! and most just say their names when you select them, as opposed to the Sonic characters who actually have quotes.
Highlight of the experience: Sonic in the swimming events. He's the only character with a life vest, and for his swimming animation, he just runs in the water while using the vest to float. It's goofy as hell, and kinda neat that the developers remembered the fact that Sonic can't swim.