Plot

Portal 2 follows the player-character Chell's fate after the end of Portal. Retroactively patched just prior to the sequel's official announcement, the ending of the first game shows Chell being dragged away from the remains of GLaDOS by an unseen figure with a robotic voice, later identified by writer Erik Wolpaw as the "Party Escort Bot". She is placed in stasis within Aperture Science for a period of many years, during which the facility becomes overrun by decay and nature. The Aperture setting is part of the Half-Life series; while Portal's events occurred before Half-Life 2, the sequel takes place much later than that game. One hidden area of the game shows the former location of Aperture Science's cargo ship, the Borealis, in the bowels of the facility; this ship is mentioned as part of the Half-Life universe at the end of Episode 2, having been discovered in the Arctic, situated in a seemingly-impossible position with all hands lost. Portal 2 suggests the ship was related as a result of an experimental teleportation device being developed by Aperture to compete with Black Mesa Research Facility, a competitor featured in Half-Life.

Portal 2 Gameplay

A representation of how the magnitude of linear momentum is conserved through portals. By jumping into the blue portal, the character is launched out of the orange portal and onto the platform on the right.

A more advanced portal technique. The character builds up speed using two blue portals, to reach an otherwise unreachable area. The second blue portal is carefully created mid-air, after exiting the orange portal for the first time, destroying the first blue portal in the process.

Portal 2 is a puzzle game presented from the first-person perspective. Normally, the player, as either Chell in the single-player campaign or as one of two robots, Atlas or P-body, in the co-operative campaign, can move, look, and carry and drop objects, as well as interacting with switches. The goal is to maneuver the characters through a number of test chambers in the Aperture Science facility, traversing the chamber from the start to the exit. Though the player-character can take some damage for a brief period of time, they will die under sustained injury and be restarted at a recent checkpoint; however, characters are equipped with "long fall boots" that absorb the shock of landing after a large vertical drop. The player must figure out how to overcome seemingly-bottomless gaps, evade pools of toxic liquid, or avoid line-of-sight or even disable robotic turrets to safely arrive at the exit.

Initial levels provide a tutorial on general movement controls and interactions with the environment. After these levels, the player will be required to solve puzzles in test chambers within the Aperture Science Enrichment Center using the "portal gun" (the Aperture Science Handheld Portal Device), a device that can create two portals connecting two surfaces across space. Players solve puzzles by using these portals to move unconventionally between rooms or to use the ability to fling objects or themselves across a distance. The functionality of the gun has not changed between the games, but within Portal 2, players can take advantage of the transmission of other physical effects through the portals. One example is the direction of Excursion Funnel tractor beams or Hard Light Bridges through portals to provide surfaces or areas which the player can use to move the player-character or specific objects across obstacles. While early technology demonstrations included the use of Pneumatic Diversity Vents, a series of transport pneumatic tubes, and the interaction of their suction or venting power through portals, these do not appear in the final game, as the technology was not quite perfected by release.

The game also introduces special paint-like gels that can be used to impart certain physical effects to a surface such as Propulsion Gel that boosts Chell's speed as she crosses a surface, and Repulsion Gel that allows her to bounce from a surface. A third gel type, Conversion Gel, allows any surface coated with it to accept portals. The player will be required to determine how to transport that gel to appropriate surfaces using portals in order to progress. The gels can also be applied to objects, such as the Aperture Science crates, that affect their own physical nature. Water can be redirected to wash away gels applied by the player, returning the surface or object to its normal state. In addition to the returning but cosmetically redesigned Storage Cube, there are new types of objects that assist the player, including Redirection Cubes with prismatic lenses used to redirect Thermal Discouragement laser beams, Aerial Faith Plates that can launch objects placed on them, and spherical Edgeless Safety Cube, which made a brief appearance in the original game in one of the advanced chambers. The heart-decorated Weighted Companion Cube, used by GLaDOS in the first game to make Chell form an emotional bond to the inanimate object before incinerating it, also appears briefly in the sequel.

While most of the single-player game takes place in the test chambers created by GLaDOS or her personality cores, there are times where the player will need to move behind-the-scenes in areas beyond the test chambers as they are reconfigured, leaving the player free of GLaDOS's observation and control.

The game includes a two-player co-operative mode in addition to the single player mode. This mode can be played by two players at the same computer/console via split-screen, or through two remote players at their own computer/consoles; Microsoft Windows, MacOS X, and PlayStation 3 users can play with each other regardless of platform. Both players control separate portal guns and can use the other player's portals as necessary; each player's portals are of a different color scheme (blue/purple, and orange/red) to help distinguish between the two sets.Because of the number of possible portal combinations, the test chambers that the players proceed through are much more difficult than the single-player campaign, requiring the two players to work together. Initial chambers set each robot in their own separate section of the chamber, and their solutions teach the use of the communication tools and portal use to complete.

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.