The value of this game is pretty amazing. There's a surprising amount to do and there's reasons to replay the levels. It looks, sounds and plays very well.
At first I felt it was a bit floaty, but you get used to this... Plus the better cars you'll eventually unlock make up for this.
I actually enjoy the multiplayer combat racing as well. No it's not as good as Mario Kart, but it works well and is currently the best alternative to that on the 360 I'm aware of.
Really am having fun with this one. Definitely a sleeper. Consider the DLC even.