Two games were demoed at the Apple Event Wednesday. Real Racing 3 was the one that really showed off the device. Talking to Rob Murray after the event he noted that the A6 processor in the iPhone 5 allowed them to turn up the effects even more than they already had to make everything in the game look even more realistic.
Real Racing 3 will be out before the end of the year and include interesting new features like time-shifted multiplayer via Game Center, working side mirrors, and visual effects like we've never seen on a portable device. These are console-quality graphics we are talking about. Take a look at the following, first screen shot of Real Racing 3 (click for full size 1136x640 screen).
I can not wait to get my hands on this one.