Since I didn't see a thread about this game already I thought I'd bring attention to it. I've been playing Killing floor since halloween of this year. I bought it on steam while it was 75% off. It has no storyline whatsoever, and isn't technically about zombies, but genetically altered people turned into monsters. The enemies called Clots, however, behave very much like stereotypical zombies.
This is a class based FPS game that is loads of fun to play with friends, and it has dynamic difficulty that adjusts for the number of players connected to your server. Since I'm not so great at describing stuff like this I'll just link you over to a gameplay video in case anyone is interested in checking it out.
I thought you were making a reference to the blues tune "Hard Time Killin Floor Blues." That's an amazing little bit of culture right there.
Regarding the game, I might give it a try once I get a computer that will be able to run games. I have a steam account but haven't used it much because I don' have any games that would run on my old computer, and not money or real reason to get a new one. Perhaps later.
I will grab fate by the throat; it shall certainly not crush me completely.
-Beethoven