Innovation in video games is terrific—sometimes. But with certain ideas and series, particularly the simplest ones, the smartest thing to do can be to just expand and build on the concept but not change it very much. That's the choice Valve Software has made with Portal 2, the ravenously awaited sequel to the addictive and brain-twisting 2007 first-person puzzler. Judging from our initial half-day with the game, Valve has chosen wisely.

The original Portal, first released as part of the Orange Box collection, was maddening because it was so straightforward, and delightful because of its rampant dementedness. As a test subject trapped in the Aperture Science building, you were armed only with a gun that could create up two dimensional portals: shoot a blue one, shoot an orange one, then run through one to emerge from the other. Strategy and physics played key roles as you struggled to discover what happened to the all the office workers, evade turret fire and pits of foul-looking liquid, and determine what the nature was of the teasing and tormenting computer (the Genetic Lifeform and Disk Operating System, or GLaDOS) that made jokes at your expense every 30 seconds.

Portal succeeded because its formula was both hard to screw up but easy to love. It was both rigorously adult (some of the levels were hard, and many of the bonus boards all but impossible), and yet faultlessly cute (who can forget the baby-voiced android weapons, or the Weighted Companion Cube emblazoned on all six sides with hearts). This meant that anyone of any age could play it, and because it required just a handful of keys or buttons (far fewer than the average shooter), you didn't even need to be an experienced gamer. As if realizing this, Valve even structured the game to provide to provide its own fully integrated tutorial so you could master tricky concepts without being aware you were learning everything.

In fact, the most commonly cited problem with the game was that it was too short: Nineteen levels and it was done. For years, people have been crying out for more levels and more snappy wit—and with Portal 2, that is what Valve has almost exclusively provided.

If you know Portal's controls, you know Portal 2's—there are no significant variations. If you remember how to perform advanced moves, such as using momentum from a vertical fall to fly across a horizontal gap, your skills will not be wasted. The graphics have been polished a bit, but have the same whimsical 1930s sci-fi serial–meets—Star Trek: The Next Generation vibe about them. Voice actress Ellen McLain, irreplaceable as the saucy and strangely sympathetic GLaDOS, is back, too. Even a handful of early levels from Portal 2's single-player scenario will look familiar if you've memorized the first game's layouts.

This is not unintentional, by the way. When the game begins, you awaken again in the testing center, and must escape with the help of the personality sphere Wheatley (voiced, with a ingratiating English lilt, by Stephen Merchant). But after revisiting a few rooms—don't worry, all are slightly different this time around—you wander into previously unexplored areas of the center and accidentally resurrect GLaDOS—who then creates on the fly new rooms for you to face, as well as myriad other troubles. There's more to the story, especially when GLaDOS and Wheatley become adversaries, but this is ample kickoff for the action.

The turrets and even the Weighted Companion Cube are back, but they haven't come alone. Thermal Discouragement laser beams threaten to saw you in half unless you deflect them with the new six-mirrored Redirection Cubes. Aerial Faith Plates are highly precise springboards that send you soaring through the air to a predetermined destination (always marked with a bull's-eye). Light bridges support you across chasms, and may be redirected with a blast of your portal gun. Blue Repulsion Gel lets you bounce to great heights without needing to fire up a portal at all; red Propulsion Gel gives you an extra boost of speed to accomplish difficult maneuvers.

These new elements integrate seamlessly, allowing for new tactics and techniques, but they still leave your brain and your portal gun to muck through most of it on your own. And if you're concerned that all these new tools will make the game easier, think again: Portal 2 is also harder, packed with more and larger levels than the original, with some especially fiendish in the degree to which they rely on a combination of applied understanding of the Portal world and, well, dumb luck.

In addition to the single-player game, you can also play the cooperative mode, which drops you and a friend into the roles of robots ATLAS and P-Body as they take embark on their own story set in the Aperture Science labyrinth. There's a fair amount of supplemental material, too, to help you get the most for your gaming dollar. (The single-player campaign only runs about eight to ten hours—certainly longer than the first game's, but otherwise on the short side.)

Portal 2 is available now for PC (running Windows XP or better, with a dual-core processor, 1-2GB of memory, 7.6GB of hard drive space, and a DirectX 9 video card) and Mac (running Mac OS X v.10.6.6 or better, and packing an Intel Core Duo CPU, with at least 2GB of RAM, 7.6GB of hard drive space, and either the GeForce 8600M or ATI Radeon HD 2400 video card); the game also requires a steam account for installation, validation, and tracking achievements, and costs about $50. PlayStation 3 and Xbox 360 editions hit around $60 (although Amazon is currently selling them with a $20 credit.) You might want to set aside a few extra bucks for cake, too—GLaDOS will undoubtedly want you to have some, and given how sweet Portal 2 already seems to be, we would be only too happy to oblige her.

This article, written by Matthew Murray, originally appeared on PCMag.com and is republished on Gear Live with the permission of Ziff Davis, Inc.