Trust me, the game is fun, but get it for another system if you can.
The story is different for all the teams. Team Sonic is challenged by Eggman to save the world in three days from his newest scheme, which the team obviously accepts. Team Rose is searching for friends: Amy's looking for sonic(duh), Cream is looking for Cheese's friend Chocola, and Big the Cat is looking for froggy(again, duh). Team Dark is out for revenge against Eggman. Team Chaotix is hired by a mysterious caller, who will pay them a generous amount of money if they can save him. Team Rose is easy, Team Sonic is normal, Team Dark is hard, and Team Chaotix is normal but with harder missions.
The gameplay is broken down into parts. First, the teams are made up of three people. You can switch between these characters to use their different abilities(Sonic has speed and his homing attack, Tails has flight and an ariel attack, and Knuckles has strength to smash through enemy robots and obstacles). The object is to reach the end of the stage without dying. Simple, right? Along the way, you will sometimes temporarily level up your characters, which gives them enhanced abilities. If you manage to fill up the gauge at the top of the screen by defeating enemies, collecting rings, etc., you will be able to use the team attack, which eliminates all enemies on the screen.
The environments are nice and colorful, but not quite as good as the other systems. As for music, there are many catchy songs that add to the experience. Graphics, again, are good but not quite as good as the other systems.
Overall, this is a fun game that should be enjoyed, preferably on the gamecube. Still, it's a decent pc game, nonetheless. Enjoy!