I downloaded the demo of this game from marketplace in October 07 and have yet to get bored of it. I have been waiting and waiting for it to appear for pre-order.
This is one of the greatest alternative driving games I have ever played, there is a great variety of vehicles, terrains and game types, and you can just pick up and play or go for the full on career mode. You can freestyle, moto-x, waypoint race or go cross country. I've tried the moto-x bike, the quad, and the buggy and they all handle and perform differently. Looks like there will be monster trucks in the full version ... how cool is that!
Graphically this game is pretty good, but it's just the sheer fun element of the gameplay that makes this a must own. Pre-order it now, you won't be disappointed.