Almost four years ago, Valve released Portal, a unique genre-blending puzzler that had flown largely under the radar and took everyone by surprise, far surpassing all expectations. The obstacles were deviously clever, increasing in both variety and difficulty the further you went along. The plot was minimal, with only one speaking character, but what a memorable character that was, and Portal was rightly lauded as one of the best-written games of that (or any other) year. Yet even after such an overwhelmingly positive debut, Valve wisely took its time in making Portal 2, a game that has many more expectations to meet than its predecessor. After all the praise that has been heaped upon the original, can the sequel really live up to the hype? Fortunately for all of us, it certainly can. There’s no need to be subtle: Portal 2 is as close to perfection as a game gets, regardless of genre.

Before going further, it’s important to mention that Portal 2 really is a sequel in every sense of the word. Everything, from the story to setting to puzzles, is built on the foundation of the first game. Portal 2 is so well designed that newcomers will likely still make their way through without much confusion, but why would you want to? If you are one of the three people who find themselves intrigued by Portal 2 but haven’t played its predecessor, stop reading right now and go purchase a copy of the original. You’ll be doing yourself a big favor, as it’s very reasonably priced at this point and not only is it one of the best games ever made, you’ll be ready for more when you’re done. And more is exactly what you’ll get, in some grand and exciting new ways.

In Portal 2, you once again play as Chell, the mysterious female protagonist who only barely survived her training the first time around. Despite having attained her apparent freedom at the end of her ordeal, Chell now finds herself back inside the Aperture Science testing facility. The reasons for this reversal are left unexplained, but those curious about the backstory between games can read the ”Lab Rat” comic released by Valve. As far as Chell knows, her experiences in Portal 2 begin in a small room that’s been keeping her in a cryogenic sleep for who-knows-how-many years. She is awakened by a British-accented, high-strung A.I. named Wheatley, who looks like a basketball-sized chrome ball with a single, glowing blue eye. Wheatley informs Chell that they need to escape and insists this can only be accomplished together. As they make their way through the now-decaying facility, Chell finds herself having to pass through previously unexplored test chambers with the portal gun. The seemingly dead facility isn’t quite as inert as it first appears, however. Fans of the first game will be entirely unsurprised to learn that GLaDOS, the rogue A.I. from the first Portal, is very much still alive.

The entire game plays exactly like a first-person shooter, except the only things you ever shoot are interconnecting portals. On PC, you’ll move Chell with the WASD keys and pan the camera with the mouse. Point the crosshair at an appropriate wall, ceiling, or floor and click the left button (or corresponding gamepad button) to produce a blue portal. Point at another surface and hit the right button to produce an orange portal that connects directly to the blue one, wherever it may be. The concept is as simple in theory as it was in the original, but in practice it becomes far more complicated. The first game often focused on using portals to guide energy balls into receptors to power devices and experimented quite a bit with momentum. Drop from several stories high into a portal on the floor, for example, and you’d watch yourself shoot out the other strategically-placed portal to reach that otherwise-unreachable ledge. Portal 2 builds on both of these mechanics (though the energy balls have been replaced with lasers), while also adding a tremendous amount of new material.

This time around, moving tubes of air can be ridden to reach high or distant areas, while solid bridges of light can now be redirected through portals to help cross chasms and pits or block hostile turrets from firing at you. Colored gel runs from giant faucets in some later levels, which can be splashed on certain surfaces to increase Chell’s running speed or give her jumps a boost. And a new type of floor panel catapults whatever lands on it in a predetermined path. All of these elements on their own make for some pretty complex and entertaining challenges, but after the facility’s superb built-in training guides instruct you how to utilize them, the game starts to combine all the elements together into some real brainteasers. At first I thought I was going to have to criticize the game for being too easy, but then I got to the later levels and realized that Portal 2 had simply been preparing me for what was still to come.

Most of the challenges “simply” involve getting an exit door to open and then guiding Chell to the door itself. This often requires finding a way to acquire boxes to weigh down pressure buttons, and sometimes a new type of cube that redirects lasers shot into it. The obstacles to overcome are many and varied. High platforms, bottomless chasms, and shimmering blue fields that disintegrate any object you try to pull through them are among the more benign difficulties. Later you’ll come across stationary but ever-vigilant turrets which will fire on Chell if they catch sight of her. Death is only a minor inconvenience, however, as you merely have to start the puzzle over if it happens. Like in the first game, it’s important to note that Portal 2 does not require an itchy trigger finger or honed reflexes. Almost all dangers are surpassed more with thorough planning and clever thinking than how fast you react. While the interface may be different from more traditional adventure games, the puzzles once again focus on brains, not brawn.

As challenging as the single-player campaign eventually gets, it never reaches an epic level of difficulty. That pleasure is reserved for the impressive co-op campaign. In this new feature, you and a friend can connect through the Internet to play as test robots that GLaDOS is putting through her challenges. Both of you have a portal gun, but if you think that only doubles the possibilities then you’re underestimating the creative minds at Valve, as the degree of puzzle opportunities seems almost squared at times. The designers clearly believe the old adage that “two heads are better than one” and set the difficulty accordingly. Setting up your respective portals at exact locations and performing actions with precise timing is often the only way to solve many of the test chambers, and they only get harder as you progress.