The characters can be moved around freely and they can aim in any direction. While exploring, they discover chests with different types of colours. Red ones provide a score multiplier and yellow ones contain gold. The colours alternate so it is possible to wait to get specific content. The multiplier is kept going as long as the character is not hit and high scores are tracked on global leaderboards. There is also a larger online metagame where players are grouped per country and work together to eliminate their country's infection. When complete, a new cycle starts. The money collected during missions, from chests or killing zombies, is used to buy and upgrade weapons in shops found on the maps. The weapons include a rifle, mines, grenades, a submachine gun, a flare, a flamethrower, a blade cannon etc. Weapons upgrades include the rate of fire, power, clip size and max inventory. The character armor is determined through strength, endurance and agility. For each aspect different types of armor upgrades are available and these can be swapped.
Zombies usually appear in large swarms and often the characters have to fight off large waves until a certain condition in the environment is met. There are various types of zombies and new ones are introduced gradually. It is possible to interact with the environment, for instance by shooting a car to make the alarm go off to attract zombies. Vending machines provide a health pack, but the machines can also be shot to lure zombies along with other actions that cause sound. There is a melee attack and additional money is provided when a zombie is killed up close. Money can also be earned by stomping on health packs instead of using them or by melee attacking the trunks of cars.
Next to the main campaign, it is possible to play single missions. A free March 2011 update for the game added voice chat, laser sight upgrades and visual indications for when the rush meter fills (to escape quickly) or when the characters suffer damage.
