Portal 2 is the single greatest video game I've ever played.
I think, in order to give context for what I'm about to say, I should first give a little background. I've been playing video games for twenty-one years now. Between all the games I've bought since I moved out and the games I rented when I was living at home, I've probably played over a thousand video games by now. In addition to that, for fifteen years I've held the SNES RPG Earthbound as the greatest game ever, thinking it utterly incomprehensible that any game could ever surpass its greatness.
That day has now arrived. And the game is Portal 2. Portal 2 is now the greatest game I've ever played. A 10 just wouldn't do it justice. This one goes to 11. Or at least it would, if GameSpot didn't cruelly cap the possible scores at 10.
Before I open the floodgates and start talking about what this game did right, let me bring you up to speed if you're unacquainted with it or its predecessor. The main gameplay mechanic in the original Portal, which obviously returns in this game, was a portal gun that opened a blue portal and an orange portal on white walls. The two portals directly connect the two walls on which they appear: walking through one will cause you to emerge from the location of the other, and vice versa. The portals are treated just as holes in the wall: travelling through a portal with considerable momentum (such as from a fall) will give you the same momentum in the direction the other portal is pointing, as though you had just fallen through the floor into another room. This opens the game up to considerable physics-based puzzles, employing such mechanics as putting a portal at the bottom of a pit and another at the top of a wall and then falling through the former to launch yourself in the direction of the former, thereby clearing a pit in the middle of the room. The game also contained certain other objects that you needed to interact with via portals, such as boxes and turrets, which added to the puzzle potential.
That all returns in full force in Portal 2, but it's not alone: it carries with it several other newly introduced mechanics, such as a "hard light bridge", which is a beam of light that can be walked on, and "repulsion gel", which makes the floor very bouncy. All of this can, of course, be put through portals just like anything else. By the time you're putting a lot of this together, puzzles can and do get very complicated - which is all the better for one who likes a good brain-cruncher.
The story in the original Portal was largely very rudimentary. You played the part of Chell, a lone survivor in Aperture Laboratories, who is put through a series of tests by GlaDOS, a sentient artificial intelligence in charge of the entire facility, and one that has a rather sadistic streak. At what was to be the final puzzle, Chell finds herself heading towards an incinerator, but escapes, finds her way to GlaDOS' chamber, and destroys the machine, escaping in the process.
Portal 2 jumps into the future, where Chell has been taken back into the laboratory - but, due to malfunctions, the laboratory starts falling apart with her in the middle of it. A friendly, if twitchy, personality core named Wheatley comes to bust her out of there and escape. They very nearly make it out, but, thanks to Wheatley's incompetence, instead manage to reboot GlaDOS, who promptly begins to test Chell again. Thus Chell's second journey to escape from Aperture Laboratories begins.
That's the game in a nutshell. So, what does it do right? Well, um, everything.
For starters, the puzzles are easily just as good as in the first one. All of the aspects that meshed so well from the first one are back, and are augmented with several new ones. As with any game that relies on the precise balance and synergy between its composite elements, adding new things to the equation is always tricky business. Will one of the new elements end up breaking the game? Will one dominate the puzzles, leaving little room for the other mechanics? Will one end up too specific and be seen as a one-time gimmick? These are all very important questions a designer has to ask when considering adding something new to a formula that worked, and it's obvious that Valve thought of these questions, as the answer to each of them in Portal 2 is "no". Everything Valve added in Portal 2 has a purpose, meshes and interacts well with the already-existing mechanics, and feels like it fits perfectly. In that respect, Portal 2 is exactly what a sequel should be in terms of gameplay: augmented, yet familiar; fresh and new, yet retaining the winning aspects of the old.
The story is also leaps and bounds beyond the original Portal. Of course, considering the meagre nature of the story in the original Portal, an actual existant story would've already been an improvement, but Valve pulled out all the stops.
First, there are now two characters who directly interact with the player - that being Wheatley and GlaDOS - and several other more minor brushes against sentience or other life occur during the game as well. The chemistry between the characters in the game is absolutely perfect. Whereas in the first game GlaDOS was little more than a detached voice for much of the game who provided comic relief, Wheatley and GlaDOS directly interact both with the player and with each other, to great effect, GlaDOS being the calm, sadistic evil one and Wheatley being the bumbling, excitable, friendly one. The two combine to give the player very real purpose within the game, which was something that was not present in the original Portal, in which one went through the tests at least initially more or less because they were there.
Second, the narrative, as well, is miles ahead of the original Portal. While the first game did have the single plot twist in the form of GlaDOS trying to kill you halfway through, it didn't have much of interest in the story beyond that, and any narrative was more or less just an afterthought that served to tie the game together rather than being anything central. This has completely changed in Portal 2, whose story is genuinely interesting, genuinely engaging, and genuinely... well, genuine. Over the course of the game, you'll find out about Wheatley, about GlaDOS, about Aperture Laboratories, and even about things that in the first game were just purely arbitrary rules for the sake of gameplay, such as why portals could only open on white walls.
Of course, a much stronger story would be a case of one step forward, two steps back if the increase in exposition resulted in a decrease in gameplay quality. Thus, I'm happy to report that that isn't the case. In fact, Portal 2 has the single most immersive form of storytelling that I've ever seen in a game. With two extremely minor exceptions, there are no cutscenes in the game; every single little bit of story that the game tells happens exactly as you would experience it if you were there. Characters will talk to you as you're walking by something, or after something happens, or while you're doing something, all while you still have free reign over your movements and actions.
A lot of the story, as well, is entirely optional. If you don't care about the story, you're welcome to ignore almost everything that the characters actually say, and it won't affect the actual gameplay. If you do care about the story, however, there is plenty to be both heard and seen - a good portion of the story is implied in scenery that you go by rather than being beaten over the head with it by characters vocalizing it. This made the progression of the story an immensely satisfying and engaging experience, as I really felt like I was a part of it as it unfolded, as opposed to being merely an observer watching it happen.
The atmosphere in the game is also incredible. As an interesting nod to the first game, the first few areas you go through are directly from the first game - except, given the length of time that's elapsed, they're all very dilapidated and overgrown. When I first came across GlaDOS' lair and found her inactive on the ground, and when I looked around the room and into the distance, I couldn't help but have a certain feeling of awe come over me, despite the logical portion of my brain telling me that it was just a game. Throughout the game, you'll find yourself in old places, new places, polished places, run-down places, high places, low places, and everything in between; the game is a marvel of level and atmospheric design.
The clever and dry writing from the first game is also back in full effect. GlaDOS is the same as ever, and Wheatley provides an absolutely perfect foil to her demeanor. In addition, prerecorded announcements at the beginning let the player know exactly what kind of game they were about to play ("This next test applies the principles of momentum to portals. If the laws of physics no longer apply in the future, God help you."). The game is funny at times, serious at others, in between at even further points, but one thing remains the same: it is always, always pitch-perfect. It's not so funny that the more detailed narrative becomes a bore, yet it's also not so serious that some charm from the first game is lost. It in short blends intrigue with laughter to wonderful effect.
If there were one place where I'd imagine people might find fault in the game, that would probably be its length. The single-player mode can probably be completed in a matter of about eight hours. However, there are a ton of secret things to find in the game; there is a co-op multiplayer mode that is excellent fun with a friend that takes about the same length of time to complete; and, hell, I almost already want to play the game a second time. As such, I really can't fault the game for its length. It did exactly what it wanted to do in the time it allotted for itself, and in my view, it neither outstayed its welcome nor left me hanging after ending too soon. And even if it had been genuinely only eight hours in length, it would've still been the greatest eight hours I'd ever played.
The environment in the game is complimented, as well, by the game's soundtrack. The music in the game is very much atmospheric as opposed to prominent and driving (with one exception, in which a driving song really works), but it's very moody, and sets the stage very well, conjuring up just the right emotion of ominousness, uncertainty, or apprehension, to serve as a perfect counterbalance to the humorous quirks of the characters involved.
There isn't really much more I can say about this game. I've already given the summary: Portal 2 is the greatest game I've ever played. If you enjoyed Portal, for God's sake get this game right this instant. If you didn't enjoy Portal, Portal 2 might just convince you to like it (although it might not, of course). If you haven't played Portal yet, you should try it out if it at all interests you before coming to this game - but don't spend too long playing the original, as every minute spent playing the first is a minute you're depriving yourself of the second.