I know you're probably referring to the main Sonic series of games, but I think its worth mentioning that this is a great game
Totally agree with both these posts. Sonic 3 and Knuckles was the best in the series. It was colorful, the bosses were tough and required strategy and timing, the power-up were great and added a whole new level of playability, and on top of all of that Hyper Knuckles, 'nuff said.
And the Sonic & All Stars Racing series is now something I'll really pay attention to after the second installment. It really is the closest thing we're ever gonna get to Mario Kart on the X-Box and it's a really good substitute.