Bit of discussion about it in the console section http://forums.overclockers.co.uk/showthread.php?t=18015920
Seems like its failry average (read two 5/10 reviews), apparantly while the size of it is fairly impressive, there just isnt enough reason to use the vast landscape and that the AI generally only stick to one or two paths for races. Ashame really, was looking forward to it.
There are plenty of positive reviews around:
Edge - 8/10
TeamXbox - 7.8/10
Guardian Online - 4/5
Times Online - 4/5
OXM UK - 7/10
PSM UK - 8/10
The vast majority of user reviews on the Codemasters FUEL forum have also been very positive.