Portal 2

Portal 2 is a first-person action/puzzle game, developed by Valve Corporation. It is the sequel to the critically acclaimed 2007 video game Portal and was announced on March 5, 2010, following a week-long alternate reality game based on new patches to the original game. Though initially slated for release in the last quarter of 2010, the game was postponed to the week of April 18, 2011. The game was released by Valve through Steam for Windows and Mac OS X, while the PlayStation 3, Xbox 360 and retail Windows/OS X versions of the game are distributed by Electronic Arts. All versions of the game became available simultaneously.

Story
Chell, the protagonist (player), awakes in what appears to be a dilapidated motel room. An automated announcement declares that she has been in "stasis" for fifty years and guides her through the bare minimum of mental and physical activity. Afterwards, Chell goes back to sleep.

Chell awakens again in the same room. This time, however, it is apparent that a significant amount of time has passed. Soon, she meets Wheatley, a personality core, who guides her through old test chambers from the first game in an attempt to escape the facility after its reserve power is depleted. They accidentally awaken the dormant GLaDOS while attempting to restore power to the escape pods. She separates Chell from Wheatley and begins rebuilding the laboratory.

GLaDOS subjects Chell to new tests until Wheatley helps her escape again. They sabotage Aperture's production of turrets and neurotoxin to prevent GLaDOS from killing them, then confront GLaDOS and perform a core transfer; replacing her with Wheatley as the laboratory's controller. Wheatley, immediately driven mad with power, installs GLaDOS on a potato battery. GLaDOS tells Chell that Wheatley was designed as an "intelligence dampening sphere" to deliberately produce illogical thoughts and hamper her own intelligence. Infuriated, Wheatley inadvertently destroys the lift to the surface with Chell and GLaDOS inside, causing them to fall to the laboratories' abandoned lowest levels.

Chell retrieves the potato battery and they form a reluctant partnership to stop Wheatley before his incompetence destroys the facility. Ascending through laboratories built in the 20th century, they discover audio recordings by eccentric Aperture Science founder Cave Johnson. The recordings reveal how Aperture slowly lost money and prestige throughout the decades, as its pool of test subjects was altered from "astronauts, war heroes, and Olympians" in the 50's, to homeless people in the 70's, and Aperture's own employees in the 80's. In 1981, Johnson became mortally ill after ingesting moon dust used to manufacture portal-conductive surfaces. His last request was for the mind of his assistant Caroline to be transferred— by force, if necessary— to an advanced computer designed to store a human consciousness, which he had previously commissioned to save himself, creating GLaDOS. GLaDOS is troubled by the discovery that she is Caroline.

Chell and GLaDOS return to Aperture's higher levels, where they discover Wheatley's utter incompetence has brought the Aperture facility on the verge of catastrophic failure. Wheatley, after discovering Chell and GLaDOS had returned, decides to keep them alive as test subjects because the "franken-turret" cubes he created were ineffective at solving tests. GLaDOS later reveals that her body came built-in with a euphoric response to test completion that becomes less effective over time. Throughout the following chambers, Wheatley becomes increasingly frustrated with its dwindling effects.

Wheatley reveals that he has a "surprise" for Chell and GLaDOS, later tricking them into a death trap. He reveals that he had discovered the two robots from the Cooperative Testing Initiative, the game's cooperative campaign, making Chell no longer useful to him. She manages to escape from the trap right before its activation. The game's final levels are spent escaping from Wheatley's numerous attempts to kill them.

In the game's boss fight and ending, Chell confronts Wheatley and attaches corrupted personality cores to force another core exchange and restore GLaDOS to authority. However, Wheatley demolishes the button necessary to initiate the transfer. As the facility crumbles, Chell places a portal on the Moon; she and Wheatley begin to be pulled into the vacuum of space. GLaDOS, having reasserted control over the facility, rescues Chell and abandons Wheatley to outer space. When Chell awakens, GLaDOS claims to have learned of humanity from the remnants of Caroline, but deletes Caroline's personality. Deciding that Chell is not worth the trouble of killing, GLaDOS frees her from the facility.

In a post-credits scene, Wheatley, still trapped in space along with the “Space Core”, voices his regrets about betraying Chell.

Gameplay
Portal 2 continues to challenge the player through numerous platforming and physics-based puzzles using the Aperture Science Handheld Portal Device (the "portal gun"), a device that can create a temporary wormhole between almost any two flat surfaces. Other gameplay elements are added to Portal 2 including tractor beams, laser redirection, and special paint-like gels, taken from the Independent Games Festival-winning DigiPen student project Tag: The Power of Paint, that imparts special properties to objects it touches, such as increased momentum. Portal 2 also includes a two-player co-operative mode in which each player-character is a robot that has become self-aware due to GLaDOS' influence, and requires both of the player's teamwork with their own portal guns to complete each level.