Killing Floor is a cooperative first-person shooter developed and published by Tripwire Interactive. The players assume the roles of the members of the British military and police, tasked with fighting an invasion of bioengineered mutants, swarming the streets of London. The game features two modes - Jilling Floor and objective - each with its own rules and victory conditions. The game received solid reception from the critics, who noted that the game wasn't free of flaws, but provided enough entertainment value to overlook them. 

Gameplay

The gameplay mechanics of Killing Floor game are divided between two distinct modes. In the Killing Floor mode, the players must deal with waves of increasingly stronger enemies, culminating in a fight with a boss creature, the Patriarch. In Objective mode, the players are given a series of tasks to complete, for which they are rewarded with money they can spend on weapons, among others. 

KF emphasizes cooperation between the players, with many actions that can help the team survive the waves of monsters, including healing and welding te doors,   working better on the player's teammates.

Each player can choose a specific perk at the beginning of a level, which boosts certain stats such as the effectiveness of healing and aim precision. The player can upgrade their perks by using them often enough or by simply playing through the level and not dying. 

As with other games of the FPS genre, Killing Floor gives the player an arsenal of deadly tools to unleash on the mutated hordes, such as assault rifles, shotguns, flamethrowers, etc. The weapons can be purchased for the in-game money or found throughout the level. Increasing the levels of the player's perks can boost the effectiveness of a given firearm. 

Story Summary

In the near future, Horzine Biotech is contracted by the military to conduct experiments on human genetic material and military applications of cloning. The results of their research are ZEDs, violent, zombie-like monsters. When an incident causes the ZEDs to be unleashed upon the streets of London, neither the British army nor the London police are able to stop them. As the plague spreads across the city, the remaining members of London's finest and British special forces rally to enter Horzine's headquarters and put an end to the ZEDs' invasion. 

Reception

The reviews of Killing Floor were mixed but generally positive. The critics noted the games flaws, including paper-thin story and shoddy voice acting, but praised the gameplay mechanics and interesting ideas the developers tried to convey. The game reviewed accolades, including the 2009 Voodoo Extreme's Reader Choice Award for Overall Best Game of the Year. 

Key features:

• Two distinct gameplay modes emphasizing cooperation between the players  
• A variety of destructive weapons available to the player 
• An interesting system of perks the players can equip