It's a classic.

Confucius say: man who whip pussy will not get pussy whipped.

Gameplay: 7/10
Visuals: 9/10
Updates: frequent
Audio: 8/10
Overall: 7/10

This game has many features including quality updates, amazing graphics, chilling audio, and overall a good zombie game.

The things that stop me from giving the game a higher overall is the fact that the zombies can be challenging in solo, or even in co-op. The beginning zombies are able to grapple you, stopping you from moving when they are alive (clot), making it particuarlly difficult. The other are, of course, crawlers. These things never get off of you. Upgrading system is very slow to level up (1-6), sometimes taking a full 15 games to level up once, getting harder every round.

Pros: upgrading and leveling up, amazing graphics and sounds, overall good balance, and co op is great.
Cons: upgrading system is very slow, some zombie types have a clear general overpowerment VS. human players.

I highly reccomend Killing Floor for its addictive features, great graphics, and plain fun slaying.