Finally, a reason to use my PS3 for more than watching movies.
This one appears to be an instant classic. Imagine a Mario Kart style game, with the ability to create your own levels, and characters.
I spent over an hour just playing around with the track editor. The interface is very simple, you create a track by driving around. It's simple, and it works very well. You can tweak things like width after the track is done.
You can use an auto populate tool to place scenery, power-ups, and obstacles, or you can meticulously place every item manually.
The ability to play other PS3 users custom levels means this game will have a ridiculous amount of longevity.
It's the same "play, create, share" concept Sony introduced with Little Big Planet, except in this case level creation is much easier and accessible to even the most casual player.