Grand Theft Auto IV is an action-adventure game played from a third-person perspective. Players complete missions—linear scenarios with set objectives—to progress through the story. It is possible to have several active missions running at one time, as some missions require players to wait for further instructions or events. Outside of missions, players can freely roam the game's open world, and have the ability to complete optional side missions. Composed of the fictional city of Liberty City, the world of Grand Theft Auto IV is larger in area than most earlier entries in the series. At the beginning of the game, players can only explore the first island–composed of Dukes and Broker–with all other islands unlocking as the story progresses.
Players use melee attacks, firearms and explosives to fight enemies, and may run, jump, swim or use vehicles to navigate the game's world. There is a first-person perspective option when using vehicles. In combat, auto-aim and a cover system can be used as assistance against enemies. Should players take damage, their health meter can be fully regenerated using multiple techniques, such as eating, using medical kits, or calling for paramedics. If players commit crimes while playing, the game's law enforcement agencies may respond as indicated by a "wanted" meter in the head-up display (HUD). On the meter, the displayed stars indicate the current wanted level (for example, at the maximum six-star level, efforts by law enforcement to incapacitate players become very aggressive). Law enforcement officers will search for players who leave the wanted vicinity. The wanted meter enters a cool-down mode and eventually recedes when players are hidden from the officers' line of sight.
The player character positioned in cover behind a vehicle, preparing to shoot at police officers on the other side of the vehicle.
Combat in Grand Theft Auto IV was reworked to include a cover system.
The game's cover system allows players to move between cover, to fire blindly, aim freely, and target a specific enemy. Individual body parts can also be targeted. Melee attacks include additional moves, such as dodging, blocking, disarming an opponent and counter-attacking. Body armour can be used to absorb gunshots and explosive damage, but is used up in the process. When health is entirely depleted, gameplay stops, and players respawn at the nearest hospital.
The game's single-player mode lets players control a war veteran, Eastern European Niko Bellic. During the story, Niko meets various new characters, many of whom he befriends. These characters can then perform favours for Niko whenever he asks; for example, his cousin Roman, who owns a taxi service, can send one of his cabs to Niko and take him to any destination around the city. Cabs are always available during gameplay, allowing players to quickly travel to a destination. Throughout the course of the game, players are also faced with morality choices, which alter the storyline appropriately depending on the player's choice. While free roaming the game world, players may engage in context-specific activities such as bowling or darts. Other available activities include a vigilante mini-game, and in-game television programming. Niko has a smartphone for contacting friends and starting activities. The smartphone is also used to access the game's online multiplayer mode, and to enter cheat codes. To access the in-game Internet, which allows Niko to send and receive emails and set up prospective dates with potential girlfriends, Niko can use Internet cafés located around the city. The game also features a subway system, allowing players to quickly traverse through the game's world