Batman: Arkham City, players have expressed frustration with severe performance issues encountered in the game. Warner has confirmed that a stuttering framerate is tied to DirectX 11 features, which should be disabled while a patch finds its way to Gotham's cordoned-off criminal depository.
Disabling DirectX 11 (under "Settings" in the Games for Windows launcher, and "Configure PC Options" in your Steam library) will drop the game down to DirectX 9. It's not as disfiguring as it sounds, but let's not make excuses for a game launching in such an unsteady state. We'll be sure to let you know when the punitive effects of tesselation and horizon-based ambient occlusion have been eliminated.