Looking at the in-game footage, lighting while in-game is definitely downgraded, and much more like Forza 2. The cars still bleach out when reflecting light. I don't think this has 'real' HDR? Lighting in in-car view seems even more flat. Still 8 cars on track also, it seems. I like the art-design on this track in general - Forza has always been pretty good at that - and the cars look a bit better than in Forza 2, though in-game I don't think the cars have that many polys to be honest, 100.000 maybe including cockpit? It's in the presentation screens where the cars clearly have a lot of detail. Not that this is greatly important - for me all Forza needs to do is nail the driving model a little bit better than they have before.
Only 8 cars right now is my biggest gripe with the game I think, and the lighting in-game next.