Portal 2

Portal 2 is a first-person perspective puzzle game. The player takes the role of Chell in the single-player campaign, as one of two robots—ATLAS and P-Body—in the cooperative campaign, or as a simplistic humanoid icon in community-developed puzzles. Characters can withstand limited damage but will die after sustained injury. The goal of both campaigns is to explore the Aperture Science Laboratory—a complicated, malleable mechanized maze. While some parts of the game takes place in modular test chambers with clearly defined entrances and exits, other parts occur in behind-the-scenes areas where the objective is less clear.

The initial tutorials guide the player through movement controls and interactions with their environment, and in the case of the cooperative campaign, interactions with the other player. Gameplay revolves around the use of the Aperture Science Handheld Portal Device, which can create a pair of two portals on suitable surfaces through which the player or objects can pass through. Characters can use these portals to move between rooms or to "fling" objects or themselves across a distance.

The Portal series shares a fictional universe with the Half-Life series. The events in Portal take place between the first and second Half-Life games, while most of Portal 2 is set "a long time after" the events in Portal.

Before Portal, Aperture Science conducted experiments to determine whether human subjects could safely navigate dangerous "test chambers", until the artificial intelligence GLaDOS, governing the laboratory, killed its employees. At the end of the first Portal, the protagonist Chell destroys GLaDOS and momentarily escapes the facility, but is dragged back inside by an unseen figure later identified by writer Erik Wolpaw as the "Party Escort Bot". A promotional comic shows estranged Aperture Science employee Doug Rattmann, who used graffiti to guide the player in Portal, placing Chell into suspended animation to save her life, until the beginning of Portal 2.

After the success of Portal, Valve decided to make Portal 2 a standalone product, partly because of pressure from other developers within Valve who wanted to work on a Portal product. Work began almost immediately after the release of Portal. Valve committed more resources to Portal 2's development than they had for the first game; Portal had a team of seven or eight people, but Portal 2 had a team of 30 or 40. The initial team of four was expanded as subgroups formed to devise game mechanics and to plot the story.

Participants in internal review processes were inspired by what they saw to join the project. According to Erik Wolpaw, some Portal 2 developers worked on the Left 4 Dead games to help them meet milestones, but returned to Portal 2, "with extra people in tow." Kim Swift, Portal's designer, left Valve for Airtight Games halfway through Portal 2's development.

Portal 2 was a strong favorite of gaming journalists during closed-door previews at the E3 2010 convention. The Game Critics Awards, selected by journalists and critics, awarded Portal 2 the title of Best PC Game and Best Action/Adventure Game, and nominated the game for Best of Show and Best Console Game. IGN named Portal 2 as its Best of E3 for PC, Xbox 360, and PlayStation 3 systems and Best Puzzle Game, and nominated it for Best Overall Game. GameSpy named Portal 2 the Best Overall Game and Best Puzzle Game of E3. Portal 2 won the 2010 Spike Video Game Award for "Most Anticipated Game for 2011".

Portal 2 received universal acclaim upon release. Several reviewers identified Portal 2 as an early contender for "Game of the Year", while others called it one of the best games of all time. Upon release, the game was widely considered to be as good as or better than the original. Eurogamer's Oli Welsh said that the game avoids the normal pitfalls that developers introduce in sequels, stating that "Portal is perfect.