Much will be written about how smartly designed Portal 2 is, and that’s not to be disputed. But what particularly stands out about the game is its nonstop humor. Portal 2 is the most hilarious form of entertainment I’ve encountered so far this year. There’s a delectably British sensibility to the jokes, even though developer Valve Corporation is based in the decidedly non-British city of Bellevue, Wash. For instance, one of my favorite gags is a sign that points to two nearby destinations: the Employee Daycare Center and Neurotoxin Production Center. But let’s not get ahead of ourselves. After all, Portal 2 is, first and foremost, a physics-based puzzle game.

Set an indefinite number of years after the 2007 original, you once again control Chell, a woman who’d make Harpo Marx seem talkative. And you’re still trapped in the (now extremely rundown) research facilities of Aperture Laboratories, the shower-curtain manufacturer responsible for inventing a portal gun that can create spatial wormholes between various surfaces. At the game’s outset, Chell is awoken from an extended cryo-chamber slumber by Wheatley, a small spherical robot whose giant blue eyeball resembles a HAL 9000 computer with an Apple makeover. Wheatley, who’s splendidly voiced by the British comedian and The Office exec producer Stephen Merchant, is the most delightful artificial-intelligence program one could hope to meet, and his witty quips and general clumsiness are a frequent source of amusement.

Before you know it, Chell and Wheatley accidentally reactivate GLaDOS, the supercomputer antagonist who monitored your progress in the first game until you, ahem, “murdered” her. Suffice it to say, GLaDOS is rather upset with you about that, and she quickly starts designing a plethora of “test chambers” for you to navigate. Armed with just a portal gun, it’s once again up to you to think your way out of each room and, in the process, learn a bit more about the enigmatic history of Aperture Laboratories.

Portal 2 is essentially a series of puzzles tied together by a captivating narrative, and what puzzles they are! Most of the test chambers involve unlocking an exit door, and the solutions are initially pretty straightforward. But as you proceed through the game, the challenges escalate in difficulty until you find yourself having to utilize a whole toolbox of items, including rotatable cubes that can redirect the path of laser beams, paint-like gels that can enhance your running speed and jumping ability, and Tron-esque “light bridges” that can deflect enemy fire and help you cross obstacles. When you solve an especially demanding puzzle, you’ll consider yourself the smartest human being on the planet. And when you’re stumped for a prolonged period, you’ll swear your IQ has plummeted to that of a baked potato that’s been in the oven 37 minutes too long.

There’s no getting around the fact that Portal 2 is challenging, and some may abandon it out of pure frustration. The second act, in particular, cranks up the difficulty level at a speed that may dishearten casual gamers. But it’s not a malicious game, either, and all of the puzzles make logical sense once you wrap your noggin around them. Some players will wish that Valve had included a hint system. Had such a feature been available, however, I know I would have used it a few times for problems that I eventually solved — to my elation — all on my own. In fact, the only place Valve stumbles a little is when you’re traveling from one test chamber to the next. On more than one occasion, I had absolutely no idea where I was suppose to head next. I’d spend 20 minutes devising an overly elaborate plan involving death-defying leaps, only to realize that there was a tiny wall far, far, far away that I could have simply teleported to.

But part of the beauty of Portal 2 is solving its riddles on your own terms. While a majority of the test chambers seem to have one “correct” answer, each person will arrive at that solution in a slightly different manner. The last game that made torturing one’s own brain such an enjoyable enterprise was the indie hit World of Goo. That game was also a quirky delight, but what Valve has done with Portal 2 is altogether breathtaking. And funny as hell. GRADE: A

Note: This review applies only to the game’s single-player campaign. Portal 2 also includes a two-player co-op mode with its own storyline, characters, and puzzles.

Available on: PS3, Xbox 360, PC/Mac

Developer / publisher: Valve Corporation

Rating: E10+

Price: $59.99 (for PS3 and Xbox 360); $49.99 (for PC/Mac)