OK so tonight is the first chance I've had to spend some time playing the game. It's nice! A lot like the other Forza games but it all seems good. One weird glitch in the race in Rio - as you approach the coast you can see a Boeing 747 coming in really low to land. One moment it's there, the next it's completely gone! Then you drive a few hundred yards and it's back again!
There aren't many graphics options you can change at all. By default it was running at 1080p at medium on my system (in my signature). I put it up to ultra and it still played fine but with some stuttering. High plays smoothly with no stuttering on my system and it looks very similar to ultra.