I heard need for speed undercover was wack. The biggest complaint is how they try to nickel-and-dime you into buying content that should be unlockable in the game.
I played Midnight club LA and that game is good. Burnout Paradise is GREAT. Wipeout HD is great also. Right now I am playing Motorstorm 2 and that game is very fun. The demo does it NO justice at all. The game itself looks 20x better than the demo they released.
