I picked up Killing floor from Steam today and i must say its a whole lot of fun, i must have log about 4 hours or so on it and i want more, its like L4D in that's its a a CO-OP survival horror game but its up to 6 people instead of 4 and the whole stage is open and the Enemies come in waves getting harder as you go. All in all its a fun game for only $20 its a steal, here's a video of me playing.