I tried the demo and the physics were awesome. The changes in surfaces and stuff, the car just really felt good. Its probably how Forza would feel if it had F1 cars.
I owned 2010 and the bugs were pretty big, but the career mode and stuff was fantastic. Had I not spent stupid fake money on Forza DLC, I would've gladly jumped to another racing game, but I feel locked in now. Would definitely buy F1 once it hits 20-30 bucks. By then 2013 will be out though.