Highlighted by an expanded cast of characters, difficult puzzles, and extreme hilarity, Portal 2 builds on the foundation of its predecessor, crafting one of the most uniquely satisfying experiences of this console generation. The original Portal has amassed critical acclaim and a cult following, but one could not help but note the title's brevity. It left fans wanting more levels, jokes, characters and time in the ominous Aperture universe. Following up Portal with an equally amazing sequel would be difficult for any other developer, but Valve Software has effortlessly shattered all expectations.

Mentally reinvigorated and set for another adventure, Chell, the protagonist from the original game, awakes from a long hiatus to discover that Aperture Science's laboratories have succumbed to mother nature. Guided by Wheatley, a brilliantly-voiced anthropomorphic robot, players attempt to escape the clutches of GLaDOS, Portal's iconic, auto-tuned villain.

Ultimately, the plot of the story is not determined by cinematic cutscenes, but rather the short bits of audio that accompany each test chamber. The story gradually eases players into puzzle-solving techniques, but there does come a point where the pacing sags. This is largely due to the fact that the second act references the past very heavily, which is interesting for any Portal fanboy, but generally a snore-fest for newcomers.

In addition to the single-player campaign, Portal 2 features an equally sarcastic cooperative story that emphasizes teamwork and communication. Joining up with a friend allows players to enter into an entirely new adventure as Atlas and PeaBody, two generally-clueless robots. GLaDOS narrates this mode as well, maintaining the same expected sarcasm in her dialogue, either making light fun of the portal-solving duo or insulting the insecurities of humanity.

Valve's experience with creating cooperative titles, notably Left 4 Dead, is extremely evident throughout the well-polished experience. There are numerous commands that can be used to indicate objectives to your partner, but having a microphone is almost a prerequisite for success in this mode. Without the active collaboration of a partner-in-crime, players are left frustrated. There's no diffusion of responsibility in this game mode, meaning that both players have to be constantly engaged in the action to solve the puzzles.

One of the most memorable aspects of the Portal universe is its cast list, featuring such greats as Stephen Merchant and Ellen McLain. Wheatley, the moronic, spherical robot mentioned earlier, is absolutely hilarious throughout. Sarcastic and witty, his indecisive ambivalence towards his creators contrasts GLaDOS' complete devotion to Aperture well. Wheatley adds a human component that is extremely necessary in a title as long as Portal 2, which would otherwise become stagnant and monotonous.

GLaDOS, the omnipotent overlord of the laboratory complex, is back and as insidiously hilarious as ever. As referenced previously, her "murder" at the hands of Chell in the first Portal drives her desire for revenge. After a surprising plot twist, players are gradually introduced to new realities about GLaDOS' past, revealing her true personality.

While the second act of Portal 2 may feel drawn out and overdone, players are urged forward by Cave Johnson, the founder of Aperture Science voiced by J.K. Simmons. His gradual fall from power is interesting and well-performed, revealing bits of information about Aperture's past as well as humorous warnings regarding future obstacles.

In a state of disrepair, Aperture's laboratories come to life before your eyes, a sight that is nothing short of stunning. Minimalist in design, the title's attention to detail is admirable, immersing players in a fully-realized universe. The environments span from claustrophobic test chambers to open underground chasms. Metal can be rusted over and twisted or neat and modern, almost giving way to a variable experience that keeps the visual style somewhat fresh.

Complementing the fresh environments of Portal 2 are new gameplay mechanics as well as refined commands from the original game. The emphasis still remains on spatial puzzle-solving, as players wield a gun that shoots two linked portals through which you and objects can pass, maintaining physics throughout. Companion Cubes return from Portal, which can be placed on pressure plates to solve puzzles. Lasers and refraction cubs guide light onto special receptors that will open doors and solve puzzles. Additionally, a plethora of gels that propel you forward or give you superhuman jumping abilities add to the fun.

These mechanics are gradually added throughout the game, and combining the various elements becomes both a challenge and a joy. Though some of the puzzles may be difficult, the game is one of the most satisfying ever to hit the market. For some odd reason, the sarcastic audio that comes with completing a level creates an insatiable desire to move forward. Though some have complained about the brevity of the campaign, a normal playthrough with no previous knowledge of the challenges ahead will take eight hours or so. Tack on an additional five to wrap up the cooperative mode and the sixty dollar price tag of Portal 2 becomes justified.

Running on the same engine as its predecessor, the graphics of Portal 2 are not exactly stunning. Luckily, the title doesn't need out-of-this world visuals to make an impression on players. It's atmosphere is so unique and hilarious that the environment's textures are not the main focus. The visual impact is consistent on all three platforms it is available for, though the PC offers the greatest level of graphics customization.

Driven by the hilarious dialogue, innovative gameplay components, and challenging-yet-rewarding puzzles, Portal 2 is able to differentiate itself from the market with its atmosphere alone. The gameplay is addictive and will force you to play through both campaigns multiple times. Though somewhat similar to its predecessor, the game feels completely independent. For its ability to deliver one of the most memorable experiences of recent gaming, we award Portal 2 a well-deserved 9.7/10.