The game is really good. Been playing it for a few days now. It's not a reatil copy obviously and going to pick a real copy for online muliplayer when the game gets released. Just trying to get a little head start here.:p. Little fact: fastest car i've found so far is the Top Secret Toyota Supra, got it up to 415kph. For reference: Bugatti veyron only goes up to about 393 kph on the le mans straight. That is one thing that's a bit unrealistic about this game, it doesn't seem to count in aerodynamics.
It's definitely a big step up from Forza 2, and not just talking graphics wise. It's more fun to drive and the overall feel of the game, even including the menu and presentation is way more engaging.