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Quoted from Wikipedia:
"Portal 2 is a first-person puzzle-platform video game developed and published by Valve Corporation. The sequel to the 2007 video game Portal, it 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 fourth quarter of 2010, the game was postponed to the week of April 18, 2011. The game was released by Valve through Steam for Microsoft 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. The game's release on Steam was preceded by a second multi-week alternate reality game, the Potato Sack, involving 13 independently-developed titles which culminated in a distributed computing spoof to release Portal 2 several hours early.
Like Portal, Portal 2 primarily comprises a series of puzzles that must be solved by teleporting the player's character and simple objects using the "portal gun", a device that can create inter-spatial portals between two flat planes. The game's unique physics allow momentum to be retained through these portals, and requires the creative use of portals to maneuver through the game's challenges. Most gameplay elements of the original Portal were retained in the sequel, but many elements were added to Portal 2, including tractor beams, laser redirection, and paint-like gels that impart special properties to objects they cover. These gels were created by the team from the Independent Games Festival-winning DigiPen student project Tag: The Power of Paint.
Within the single player campaign, the player returns as the human Chell, having awakened from stasis after many years. Chell must navigate the now-dilapidated Aperture Science Enrichment Center and its test chambers with the portal gun while the facility is rebuilt by the reactivated GLaDOS, an artificially-intelligent computer that first appeared in Portal. The game has a larger storyline than Portal; Valve introduced additional characters, including Wheatley, a robotic personality sphere voiced by Stephen Merchant, and recordings of Aperture Science CEO Cave Johnson, voiced by J.K. Simmons. Ellen McLain reprised the role of GLaDOS. Music from Jonathan Coulton and The National appears in the game. Portal 2 also includes a two-player co-operative 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 chambers specifically designed for co-operation.
Though many reviewers were concerned about the difficulty of expanding Portal into a full sequel, critics universally praised Portal 2. The game's writing, pacing, and black humor were highlighted as stand-out elements, with critics applauding 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 co-operative mode."
