I've just installed the demo from Steam onto a computer using the Radeon HD 5870. The first thing I did was go into video settings and ensure that PhysX was turned off, and antialiasing was turned on. All other settings were turn on to high.
The built-in benchmark delivered 85 FPS on average, and the graphics looked meh. It seemed like maybe I missed a setting somewhere, so I returned to video options. When I did, antialiasing was turned off. So I turned it on, and ran the benchmark again. Same results.
Again, I visited the options and looked at the video settings. For some reason, the antialiasing keeps turning itself off. Is anyone else seeing this issue?