Sometimes the game runs sometimes it doesn't, sometimes it just runs very badly.

[ultio]

I'm having the exact same problem as well. I just bought the game a couple of hours ago and I played it with all settings maxed out, except for SSAO, and after taking just a 10 minute break I wanted to just jump right back to the game. But suddenly the perfomance of the game was really bad, going from pretty much constant 60 fps down to 1 fps - 20 fps. This is quite weird, you guys should look into it.

I tried what Pojoman said - restarting the computer - and that actually worked, but it's still not a satisfying resolution to the problem.

My specs:

Windows 7 Professional - 64 Bit
Purchased the game on Steam

Intel Core2Quad Q6600 @ 3 Ghz
Nvidia Geforce 8800 GTS - 512 MB
3 GB DDR2 RAM (800 Mhz)
abit IP35-Pro Motherboard
Creative X-Fi Xtreme Gamer - 64 MB - Soundcard

All drivers are up-to-date.