The gameplay consists of a single game type, single- or multi-player, in which the player fights waves of zombie-like specimens, with each wave becoming successively more difficult, moving through each area of the level, until it concludes with a battle with a "boss" specimen, called the Patriarch.
There are a wide array of weapons, including melee weapons, shotguns, rifles, sidearms and other weapons. Players may accumulate money through killing specimens, surviving waves, from other players, and selling acquired weapons. This money can then be used for weapons, supplies, and ammunition at "the Trader" on completion of a wave. The trader's location is randomised, as a mechanism to encourage players to explore the map. Current trader location is indicated to players at all times by way of a red arrow.
A feature called "zed time" allows the player to see particularly gory kills, such as headshots, in slow-motion, even in multiplayer mode. It can also give the players an advantage for a brief time to carefully aim their shots.
The "Perks" system grants the player certain strengths and abilities. The player has seven to choose from: Commando, Berserker, Firebug, Sharpshooter, Support Specialist, Demolitions, and Medic. Each are leveled up as their respective requirements are met, improving their effectiveness. When leveling up a perk, the player is not required to play with that perk.
The Commando specializes in automatic rifles and has the ability to detect invisible enemies. The Support Specialist specializes in shotguns and gains a bonus to door welding and has a larger carry weight. The Medic specializes in healing team-mates and gains a survivability bonus, including an increase in running speed. The Berserker specializes in melee weapons and has bonuses in speed and damage reduction. The Demolitions perk specializes in high explosives damage and has resistance to explosions. The Firebug specializes in fire damage, and has a resistance to fire. The Sharpshooter specializes in long-range, accurate weapons, and deals extra damage with headshots.
The game takes place in London, England.