Before I start this post I have something very important to say: The Cake is a Lie!!!!!!!! There. I said it.
Anyway, this is a Portal post. Portal is a very cool puzzle game. Well, actually there are two Portal games and both were made by Valve. Oh, and the whole "the cake is a lie" thing was popularized by the first Portal.
Anyway, this post might contain spoilers so read at your own discretion in case you want to play the game and not no a thing about the story because it is a very hilarious story. You are going to laugh out loud playing this game at least twice. Even the song that plays during the end credits is funny. SPOILERS!!!!!!
Both Portal games have are seen from the first person perspective which means you see what your character sees. But don't think this is some generic shoot'em'up (I cannot name any First Person Shooter that has something special that the none of the others have done before). This game is a puzzle solver at the core. Primarily perception based.
The reason Portal is called that is because your character has a Portal Gun. It's a gun that can place two self contained portals on almost any surface. Miracles of Science!!!!!!!!
The Portal Gun!!!!!!
I will try to avoid giving away major spoilers but in the event I do, only read if you want spoilers.
Basic Premise: There is a science/engineering company called Aperture Labs. The CEO of this company is Cave Johnson who apparently went crazy. Hence his iconic "Lemon Rant" late in Portal 2. Where he starts ranting about the "when life gives you lemons you make lemonade" phrase, then resolves to burn someone's house down with combustible lemons. Anyway, Cave Johnson has an assistant named Caroline. Mr. Johnson was dying of moon rock poisoning and intended to install his mind into the thing in the picture below.
But in a twist of fate Johnson died of moon rock poisoning before construction of "GLaDOS" started. Caroline's mind was installed in the thing in the picture above. GLaDOS is short for Genetic Life-form and Disk Operating System. GLaDOS is a computer of sorts that can manipulate the Aperture Labs building. GLaDOS was supposed to supervise all future experiments in the Aperture Labs building but the entire facility was abandoned thanks to an invasion on a rival company that makes the world seem slightly post-apocalyptic.
Anyway in the first Portal game GLaDOS is cake-obsessed, has a Cake Mix core (that supposedly teaches machines how to bake cake) and promises the player will get cake for assisting in her "experiments" (the experiments are actually puzzles). When you reach the 19th test it turns out she lied about the cake and used it as bait for a death-trap involving the floor spontaneously combusting.
This is a little fun fact. Almost every word that GLaDOS speaks in the first Portal is a lie. There is the fake cake lie that gave rise to the extremely popular phrase "the cake is a lie". Then she lies about one of the later tests being impossible. And she also lies about monitoring the player's progress, saying that from Test Chamber 4 on-wards she will stop monitoring your progress. As soon as you exit the Test Chamber she even admits that she lied to "further motivate" the player.
But in Portal 2 GLaDOS lies a lot less, but instead indirectly insults the player's character (I have no clue who you play as whatsoever). She does lie about having a surprise ready for the player very early in the game. Where she gets you hyped up for a surprise, then admits she made it up, and dispenses a cloud of confetti from a nearby tube.
And in a epic plot twist (SPOILER ALERT!) Wheatley (below), who was somewhat of a sidekick, betrays the player, turns GLaDOS into a potato battery (and inadvertently giving GLaDOS an eternal fear of crows), and takes over the entire facility in seconds. It took GLaDOS several long minutes just to get the place up and running. This is around the time the player is guided by the pre-recorded voice of Cave Johnson. Cave Johnson recorded several messages before his demise. One of which is his iconic "Lemon Rant".
Anyway, here is another fun fact. Wheatley directly references the final boss battle against GLaDOS in the first Portal and did everything GLaDOS did not do. First he made it impossible for Portals to open up on the walls and ceiling without the aid of a special gel. Second, he filled the room with nerotoxins as soon as the fight started up. Then he triggered a self destruct sequence in case the toxins weren't working properly and set the timer to 6 and a half minutes. Finally he actually bothered to make sure there was nothing the player could use to burn Wheatley (GLaDOS did not take any of these precautions at all save for the nerotoxins). But GLaDOS gives you some gel to make the walls and ceiling portal....able..... if that makes sense.
Although Wheatley survives being defeated he somehow gets trapped in space with a corrupted personality core that is obsessed with outer space (Space Core: "I'm in Space!!!").
Wow. Major spoilers. Anyway let's get to gameplay (which is just as good as story). You have to use the Portal Gun to solve increasingly clever puzzles. You can enter the portals you place down but sadly you can have no more that two portals active at a time. The Reason? Because it would be over-powered if you can have infinite portals placed down. But the good news is the Co-op story mode let's you use four Portals (two for each teammate). Just remember that the color of the Portal's edges determine which Portal you will exit through. It may sound confusing on paper but it works smoothly in action. You can place a Portal on any surfaces as long as it is.....portal-able. I am not sure if this is making sense but here goes.
Anyway, I forgot to mention that Portal 2 has a Co-op campaign. Unlike the single player where I personally have no idea who I am playing as you play as one of two robots built by GLaDOS to do the experiments that are designed for teamwork. The first robot is named Atlas and is my favorite of the two because he looks like Wheatley with legs. Then there is P-Body who has the head of one of the games hazards: The Turret. Both have Portal Guns and GLaDOS keeps track of both players scores and tallies points to each player accordingly (EXAMPLE: GLaDOS will award six or so points to the player that gets the object needed to solve the puzzle. She will stop doing this in later puzzles. She will also penalize the robots for putting each other in harms way). She also keeps track of how many steps they have taken since initial assembly, how many Portals they have placed, How many times Atlas gives P-Body a hug, etc.
Atlas (Right) And P-Body (Left).
Although GLaDOS is initially pleased with her robot replacements she quickly realizes that robots can't die, thus she cannot properly judge how deadly her experiments are.
At the end of every course she sends the duo into the lower levels of the facility to run some errands. The only way for them to return to the test chambers is to be violently disassembled then carefully reassembled. In other words GLaDOS pushes Atlas and P-Body's self destruct button. After getting quote-on-quote "worthless" blueprints, a security code with the word "blah" covering it, and a random DVD disk, The robotic test subjects open up a vault filled with millions of unconscious humans which GLaDOS plans to use for further experiments.
100,000 years later Atlas and P-Body are revived and tasked with exploring a museum created by GLaDOS. Most of the exhibits are revamped hazards, like acid pools (in GLaDOS' own words "This museum is interactive like a children's museum. Thus, the acid pools have real acid, like a well funded children's museum".). Despite the fact that the test chambers are now exhibits, they are still treated as puzzles. Also, GLaDOS will start calling her various death-traps "art".
For more info please go to the Portal Wiki. I am sorry if I accidentally gave way almost the entire story for you.