It's a lot more depending on the graphics card than previous titles, which tended to run better with a faster cpu. At the beginning, I had that weid flimmering bug as well as a little lag, it improved a lot once I updated my two month old catalyst drivers (and overclocked my card slight tad). Auto-detect put everything on ultra, with AAx4 and AFx16. I put down the resolution from 1440x900 to 1280x800, and it runs really smooth now.
Card is a 1 GB Radeon X4870, bought five months ago. My CPU is a Phenom X4 black edition @2.6 stock.