You have the entire city at your disposal, just pick your turns and you have a new track. This feature is f'ing amazing, and we will have 5 cities to design from.
I wonder if the engine could handle a free roaming mode, that would be crazy.
The fact that each city is fully realized and at your disposal is pretty damn sweet. I swear MS just keeps setting the bar higher and higher for racing games. Also, the new OXM says a true force feedback wheel will be availible near launch.