Just...one...more...race!
After searching for hours, only one feature (well, lack thereof) was found wanting, and that was the lack of a split-screen multiplayer component. It would have been nice to have seen something similar to Halo., mixing split screen and xbox-live, but you can't have everything.
That being said this is a truly solid experience for the Xbox 360. This easily defines the power of this console, and gives an idea of just what is in store for the future of console gaming: Non-stop fun at every turn. The online component is flawless and perfectly done. Both the single and multiplayer portion of the game coincide, so again, the execution is perfect. Earn some money for new cars (all of which look amazing) online and offline, and never stop having fun.
Truly a definer of its genre, you'll find yourself saying, "Just...one...more...race!" as you watch the sun come up in the morning and should have been asleep hours before.