Portal 2

Portal 2 is a first-person puzzle-platform video game developed and published by Valve Corporation. It is the sequel to Portal (2007) and was released on April 19, 2011 for Microsoft Windows, Mac OS X, PlayStation 3, and Xbox 360. The retail versions of the game are distributed by Electronic Arts, while online distribution of the Windows and OS X versions is handled by Valve's content delivery service, Steam. Portal 2 was announced on March 5, 2010, following a week-long alternate reality game based on new patches to the original game. Before the game's release on Steam, the company released the Potato Sack, a second multi-week alternate reality game, involving 13 independently developed titles which culminated in a distributed computing spoof to release Portal 2 several hours early.

Portal 2 mainly comprises a series of puzzles that must be solved by teleporting the player's character and simple objects using the "dual portal device" (better known as the portal gun), a device that can create inter-spatial portals between two flat planes. The game's modified physics engine allows momentum to be retained through these portals, which must be used creatively to negotiate the game's challenges. The game retains Portal's gameplay elements, and adds new features, including tractor beams, laser redirection, bridges made of light, and paint-like gels that give surfaces special properties, such as accelerating the player's speed or allowing the player to jump higher. These gels were created by the team from the Independent Games Festival-winning DigiPen student project Tag: The Power of Paint.

In the single-player campaign, the player returns as the human Chell, who has awoken from stasis after many years. Chell must navigate the now-dilapidated Aperture Science Enrichment Center with the portal gun while the facility is rebuilt by the reactivated GLaDOS, an artificially intelligent computer. The storyline introduces new characters, including: Wheatley (Stephen Merchant) and Cave Johnson (J. K. Simmons). Ellen McLain reprised the role of GLaDOS. Jonathan Coulton and The National each produced a song for the game. Portal 2 also includes a two-player cooperative mode, in which the robotic player-characters Atlas and P-Body are each given a portal gun and are required to work together to solve test chamber puzzles designed to require cooperation. Valve provided post-release support for the game, including additional downloadable content and a simplified map editor to allow players to create and share test chambers with others.

Some reviewers expressed concern about the difficulty of expanding Portal into a full sequel but critics universally praised Portal 2. The game's writing, pacing, and dark humor were highlighted as stand-out elements, and critics applauded the voice work of McLain, Merchant, and Simmons. Reviews also highlighted the new gameplay elements, the game's challenging but surmountable learning curve, and the additional cooperative mode. Some gaming journalists ranked Portal 2 among the top games of 2011, and several named it their Game of the Year.