Portal 2

Portal 2 retail cover art. 

Portal 2 is a first-person puzzle-platform video game developed by Valve Corporation. It is the sequel to the 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 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, culminating in a distributed computing spoof to release Portal 2 several hours early.

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 portals, requiring creative use of portals to maneuver through the test chambers. Other gameplay elements were added to Portal 2, including tractor beams, laser redirection, and special paint-like gels that impart special properties to objects they touch. Similar to how the student team of Narbacular Drop were brought into Valve to expand their game to the basis of Portal, the team from Independent Games Festival-winning DigiPen student project Tag: The Power of Paint was hired by Valve to incorporate their game's paint mechanic into these new gels.

Within the single player campaign, the player returns as the human Chell, having awakened from stasis after many years. Chell must navigate the dilapidated Aperture Science Enrichment Center and its test chambers with the portal gun while the facility is rebuilt by the reactivated GLaDOS, a rampant artificially intelligent computer. With a larger story, 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. Additional music from Jonathan Coulton and The National appear in the game. Portal 2 also includes a two-player co-operative mode in which the player-characters, the robots Atlas and P-body, must work together to complete each test chamber using their own individual portal guns.

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 comedy 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 addition of the co-operative mode.