Me personally, I would say that the only improvement to the game other then more SP content and tracks, and cars, is the visual effects. Other then that, the car feels the exact same as well do the tracks. Only exception I might give, is ABS is now better. Other then that, I still feel Race Pro has had the best physics for a racer on a console, to date, bar none. Now if we could just get the all the things Forza does good along with the things Race Pro got right,w e would have one hell of a game.
Regardless, I guarantee you that you will have a blast on Forza 3 as will I.
Again, just my 2 cp's