As Giant Bomb reports, the issue is mainly around performance. The game stutters horrendously on ATI/AMD video cards and textures take a good few seconds to pop-in. This issues are shown in this video.
id has claimed that the problems stem from driver issues, which have since been rectified with an updated driver for ATI/AMD cards, but the game is still apparently rather choppy.
This news kind of upsets me a bit. I was thinking of getting the PC version since I had presumed that would be the better one by far, but now i'm starting to consider the console versions. I've played the game for around an hour on Xbox and it is great so far. If these issues persist, it might be best to go for PS3 or Xbox if you want to get it.