Halo 2 is a shooter game. Players primarily experience gameplay from a first-person perspective, with the viewpoint shifting to third-person for vehicle segments.[4] Players use a combination of human and alien weaponry and vehicles to progress through the game's levels. Certain weapons can be dual-wielded, allowing the player to trade accuracy, the use of grenades, and melee attacks for raw firepower.[5] The player can carry two weapons at a time (or three if dual-wielding, with one weapon remaining holstered), with each weapon having strengths in different combat situations. Most Covenant weapons, for example, eschew disposable ammo magazines for a contained battery, which cannot be replaced once depleted. However, these weapons overheat if fired continuously.[5] Human weapons are less effective at penetrating shields and require reloading ammunition, but cannot overheat due to prolonged fire. Players can hijack enemy vehicles near them to quickly assume control of an enemy vehicle. The player is equipped with a damage-absorbing shield that regenerates when not taking fire; their health bar is not visible.[5]
The game's "Campaign" mode offers options for both single-player and cooperative multiplayer participation. In campaign mode, the player must complete a series of levels that encompass Halo 2's storyline. These levels alternate between the Master Chief and a Covenant Elite called the Arbiter, who occupy diametrically opposed roles in the story's conflict. Aside from variations in storyline, the Arbiter differs from Master Chief only in that his armor lacks a flashlight; instead, it is equipped with a short duration rechargeable form of active camouflage that disappears when the player attacks or takes damage. There are four levels of difficulty in campaign mode: Easy, Normal, Heroic, and Legendary. An increase in difficulty will result in an increase in the number, rank, health, damage, and accuracy of enemies; a reduction of duration and an increase in recharge time for the Arbiter's active camouflage; a decrease in the player's health and shields; and occasional changes in dialogue. Enemy and friendly artificial intelligence is dynamic, and replaying the same encounters repeatedly will demonstrate different behavior.