Bioshock 2 is a first person shooter set in a dystopian city known as Rapture. The year is 1968, following an alternative history timeline that leads the world into a dark and foreboding apocalyptic setting. The player takes control of a character called Subject Delta, who happens to be a prototype of a mostly mechanical being that takes the skin and organs of a human being and involves grafting them into a massive atmospheric diving suit. The resulting monstrosity is known as a Big Daddy, giant hulks who were created to protect the girls known as Little Sisters as they harvest a precious substance known as ADAM from dangerous areas.
There are few weapon options, but the game does allow for a variety of ammo to be used. Unique items known as plasmids can be collected and used, which give the character new abilities for attacking with. Telekinesis, shooting fire balls, and freezing are all powers granted by plasmids. Plasmids can be equipped like a second weapon, allowing players to use combination attacks. Tonics can also be collected in the game. These give the character boosts or new skills.
The main storyline follows Subject Delta's attempts to find the Little Sister he was paired with. Big Daddies are trained to protect and follow their counterparts, and Delta is the only Big Daddy to have free will. The character has no memory of the past, but is receiving telepathic messages from his lost Little Sister Eleanor. on his way to find her, the player can choose to attack other Big Daddies, which allows them to work with any Little Sister who's protector is destroyed. The player accompanies the girl around as she leads him to various sources of ADAM, and then can either escort her to the surface for possible later bonuses, or harvest her to receive a large boost of ADAM. ADAM can be used to purchase upgrades and ammo in the game.