Most of the game works perfectly fine, you can run through levels 1 and 3 without any issues, however the second level 'Nightmare' can make the game unplayable. What I did was play through it from the 'Nightmare' selection in the menu and I didn't see this happen at all during that, so I would probably recommend quitting once you get to that point and just launch it through the menu, if this doesn't help you could just open the console by using F1 and entering some cheats rushing to the meat factory section to get to the elevator or just skip the level entirely.