In the single-player campaign, players control the armored protagonist Subject Delta as he fights through Splicers—the psychotic human population of the city—using weapons and an array of genetic modifications.

Garry Schyman, who composed BioShock's soundtrack, returned for the sequel; he expanded the game's sonic palette to include more blues and religious music to parallel its themes.

BioShock 2 received positive reviews, with praise directed at its narrative, themes, art style, characters, endings and gameplay.

Players customize their character and equipped weapons and plasmids from their apartment, which serves as an optional visual representation of the game's menus.

Rapture was founded in the 1940s by billionaire Andrew Ryan to establish a city free from religious influences and government regulation.

Modified and conditioned children, called "Little Sisters", collected scarce ADAM from corpses and recycled it under the protection of armed and armored "Big Daddies".

[24][25] In the aftermath of Ryan's death during the first BioShock, the dissident collectivist Sofia Lamb and her followers, known as "the Rapture Family", assume control of the city.

Delta is informed by Brigid Tenenbaum, the custodian of the rehabilitated Little Sisters, that because he has a physiological bond with Eleanor, he will die unless he finds her.

Helped by Tenenbaum's ally Augustus Sinclair, Delta makes his way to Eleanor, who is trapped in Sofia Lamb's stronghold.

[27] Several ex-BioShock developers moved to 2K Marin, formed by Take-Two Interactive in late 2007 and based in the San Francisco Bay Area.

"[35] Early on, Thomas decided on the inclusion of the city of Rapture, which could harbor many previously unseen locations and untold stories.

[35] Thomas and environmental artist Hogarth De La Plante agreed that the setting of Rapture was fertile for new ideas and that, as veterans of Bioshock, they were excited to add never-before-seen parts of the city and continue their art style.

"Any idea was out on the table at that point, and I think nobody has played BioShock more than the developers that made it, so I feel like in one respect we are a pretty good litmus test for whether it's still an interesting place or not," La Plante recalled.

[39] The developers added more unspliced characters and offered players more decisions that impact the game's course,[36][38] with the goal of a more dynamic story and ending.

Level designer Steve Gaynor recalled that close collaboration helped gameplay spaces—and thus the world as a whole—feel functional and real.

[44] The developers limited the amount of weapons and plasmids players could simultaneously use to match the faster pace of tight multiplayer environments.

[47] Unlike the first game's questions of free will and destiny, Thomas said that the player character is "almost the ultimate individual" whom Lamb goads to fulfill her goals.

[47] Professor Ryan Lizardi draws parallels between BioShock 2's themes of community versus the individual, the extremes of Ryan and Lamb's philosophies, and the issues of McCarthyism and the hippie movement that occurred in the mid-20th century: "BioShock 2 specifically asks players to question all sides of debates when extreme stances are taken.

"[50] BioShock 2 also deals with cults of personality,[51] technocracy,[52] moral absolutism,[53] fatherhood,[51] class war,[49] equalitarianism, parenthood, childhood, and family.

[51][52][54] Character modeler Brendan George recalled their need to be careful when adapting concept art to avoid animation issues and the uncanny valley.

[33]: 17–29  Digital Extremes developed more than 26 character concepts for the multiplayer mode, eventually narrowed down to a few archetypes representing a cross-section of the Rapture population.

[57] Michael Kamper served as BioShock 2's audio lead; he joined 2K Marin after the closure of Electronic Arts Chicago.

He wrote that scoring the followup to a hit game was a challenge, and Bioshock soundtrack's praise set a high bar.

[59] Despite facing high expectations, Schyman noted having played BioShock and using an established style made composition easier.

[68][69] Over the course of a year, players were directed to a website that detailed the story of a father, Mark Meltzer, searching for his abducted daughter and ultimately discovering Rapture.

Players writing to "Meltzer" received cryptic audio recordings, and artifacts purporting to be from Rapture washed up on beaches around the world.

The content contains six maps based on locations from the main game with three levels of difficulty, seven achievements, and new unlockable concept art and videos.

The player assumes the role of Subject Sigma — another Alpha Series Big Daddy — as he travels through Minerva's Den, home to Rapture's central computer.

[109][110] Gallegos found that dual-wielding plasmids and weapons made combat less clumsy;[99] reviewers for GamePro and Computer and Video Games highlighted the new enemies as particularly well executed.

[92] Criticism included a slow start to the story[94][95] and excessive similarity with the original—Haywald wrote that the plasmid progression, and even the player character's feel, was too close to BioShock.