World at War  features more mature themes than previous Call of Duty installments and  is open-ended, giving the player multiple ways to complete objectives, but otherwise generally plays like previous iterations of the franchise. Players fight alongside AI-controlled teammates. They help during the game's missions by providing cover fire, shooting down enemies, and clearing rooms for entry.
When playing the Wii version of the game, instead of using a normal controller, such as the ones used by the Xbox 360 and the PlayStation 3, an optional gun-like expansion controller known as the Wii Zapper can be used. The Zapper, or Wii Remote and Nunchuk, can be used to aim at targets to fire at them and simulate marksmanship.
The game's return to World War II-era warfare reintroduces weapons and technology. The player gains access to these over the course of the game, but may only carry up to two weapons in addition to hand grenades. Weapons and ammo from fallen foes or friendlies can be picked up to replace weapons in a player's arsenal. Players can also find weapons with additional attachments, including guns equipped with rifle grenades, telescopic sights, and bayonets.
A character can be positioned in one of three stances: standing, crouching, or prone; each affecting the character's rate of movement, accuracy, and stealth. Using cover helps the player avoid enemy fire or recover health after taking significant damage, as there are no armor or health powerups. When the character has taken damage, the edges of the screen glow red and the character's heartbeat increases. If the character stays out of fire, the character can recover. When the character is within the blast radius of a live grenade, a marker indicates the direction of the grenade, helping the player in deciding whether to flee or throw it back at the enemy.
The single-player campaign includes thirteen hidden "death cards", denoted by playing cards attached to makeshift war graves. There is one in each level (barring those that take place in vehicles); collecting them unlocks cheats for Co-op mode, such as reduced enemy endurance and "paintball mode".
World at War's multiplayer experience resembles the one established in Call of Duty 4: Modern Warfare. All versions of the game use a similar perk and ranking system and feature six multiplayer modes, including team deathmatch and capture the flag. There are three "killstreak rewards" that can be used to turn the tide of battle: a recon plane, showing opposing players on the mini-map; an artillery strike upon an area; and attack dogs, which spawn and attack opposing players. These are gained with 3, 5, and 7 kills, respectively. They are available in all game modes, apart from team survival, and cannot be edited.
The game also features a cooperative gameplay mode with up to two players via split-screen on consoles, or four players online, for the first time in the franchise. The Wii version of the game does not include online co-op, but two players can play through a "squadmate co-op" mode which allows both players to experience the game through the same screen and point of view.
All versions of World at War (with the exception of that for the Wii) features the minigame Nazi Zombies. This is the first time the Zombies mode ever appeared in any Call of Duty game. In order to play the mode, the campaign must be completed. The mode consists of 1-4 players fighting an unlimited number of waves of Nazi zombies. Players can work together with other people to kill the zombies in a "co-op" (cooperative) mode either offline with 1-2 players or online with 2-4 players. The players gain points by injuring or killing the zombies or repairing boarded-up windows, which are used to remove blockages inside the bunker and to gain access to more useful weapons than the starting M1911 pistol and unlock more rooms. Zombies continually break the windows to gain entrance and to down the players; when all players are damaged enough to fall, the game is over. Three extra maps for Nazi Zombies were added with the World at War map packs.