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Killing Floor is a co-op survival horror FPS taking place in the devastated cities and countryside of England, after a series of cloning experiments for the military go horribly wrong. You and you friends are members of the military and police, dropped into these locations with a simple mission: survive long enough to cleanse the area of the failed experiments. The only problem is, these "experiments" aren't waiting to be taken out - they're coming for YOU.

• Cooperative gameplay for up to six players against multiple waves of specimens
• Persistent Perks system, allowing players to convert their in-game achievements into permanent improvements to their character's skills and abilities
• Over 180 Steam Achievements, including “Dignity for the dead” for killing 10 enemies feeding on dead teammates' corpses and “Hot Cross Fun” for finishing off 25 burning enemies with a Crossbow
• Slow-motion “ZEDtime” to better watch those crucial and violent creature deaths, even in multiplayer
• Solo game mode for offline play
• Ten different monster types trying to eat your face off, armed with everything from teeth and claws, to chainsaws, chain-guns and rocket-launchers
• 33+ weapons for the players to chose from, ranging from knives and fire-axes to pump shotguns, rifles and a flamethrower
• Equip your team with welders, medical tools and body armor to help your odds of survival
• Choose which Perks to play with to best balance out your co-op team against the horrors
• Open, non-linear play areas: choose when and where to fight — or run; weld doors closed to direct the monster horde down alternate corridors
• Fully-configurable, allowing players to change the difficulty level, number of creature waves, or even set up their own favorite waves of monsters
• Support for Steam Friends and other Steamworks features
• Includes Windows-only SDK for the creation of new levels and mods

Having spent many hours playing Killing Floor, I am delighted to report that it's really, really enjoyable - sometimes even more so than the amazing Left 4 Dead.
— AceGamez