How do you follow up on a four-hour pack-in title that blew up into a phenomenon that defined a year-plus of gaming culture? Valve decided to flesh out the concepts pioneered in Portal, coloring in some existing wireframes, adding details to older sketches, and doodling new expansions to previous ideas in the margins. Without turning the page, the team has painted a much richer picture that seizes your attention in a steel grip even if it’s telling a similar story.

Like the original, so much of what makes Portal 2 special is in the execution and the originality of standing in Chell’s shoes and experiencing her destiny. Any spoilers would seriously detract from the game. Not because the plot relies on contrived twists – the major beats are telegraphed in advance – but because Valve has leveraged the interactive experience perfectly. Weathering the taunts of a sadistic AI as you’re trying to survive its deadly challenges is unlike passively watching HAL-9000 try to kill off meddling astronauts. Gruesome depictions of abandoned experiments take on a new horror when you’re desperately avoiding a similar fate yourself. The dialogue’s pitch-perfect delivery is half of Portal 2’s genius, and it would be a shame to ruin the brilliant comedic timing or any of the other many nuances Valve so painstakingly crafted in this review.

This isn’t to say that Portal 2 takes itself too seriously. On the contrary, the sequel goes in a dramatically opposite direction than the Half-Life tie-in that many predicted. Descriptions of violent, painful death are played for a laugh more often than not. GLaDOS’ blithe disregard for human suffering is again a recurring comedic theme. The touch of gravitas here and there is just enough to ground the writing and serve as a contrast to Portal 2’s goofy world. I would have preferred Valve to play it slightly straighter and give a look into what catastrophic events led to the current sorry state of Chell’s world, but that’s the sci-fi nerd in me talking. We don’t need to know why the Enrichment Center is; that it is trying to kill us is enough.

I was concerned that I would tire of Portal’s one-note shtick, however amusing, over the course of a full-length game. Adding two major speaking roles and a few different environments, along with carrying over the masterful pacing of the original, keeps the single-player adventure fresh through its entire eight-hour span. I never once thought I’d place GLaDOS second on any list of Portal characters, but J.K. Simmons’ character surpasses the malevolent AI even though she’s as amusing as ever. I was never bored of the dialogue, settings, or puzzles. The constant introduction of new elements ensured that I never even came close.

The co-op campaign, on the other hand, is five hours of relatively simplistic GLaDOS banter with occasional hijinks from the cooperative testing robots. Co-op play is more mechanics-driven, with occasional bits of hilarity injected by GLaDOS’ amusing attempts to sow enmity between the two of you. The puzzles are ingenious, and the simple ability to put a marker in the game world makes plotting strategies out smooth and easy. I wasn’t sure about co-op puzzle-solving beforehand, but Portal 2 made me a rabid believer. Do whatever it takes to find someone to tackle these challenges with. They’re that good.

As for the puzzles themselves, they’re wonderful. Portal 2 has fewer agility-driven obstacles, so less dextrous gamers shouldn’t find themselves stuck on anything for lack of stick-flicking ability. The new elements are each great in their own rights, and they work together beautifully. Flying through the air after setting up a mad combination of repulsion and propulsion gel is amusing, but bending your mind around using an excursion funnel’s tractor beam to levitate the goo into a set of turrets that you had previously blocked with a hard light bridge from perforating you is amazing. The better co-op puzzles, where for example your partner is continually extending the funnel you’re both floating in via portals while you have to extend bridges between your fragile shells and passing turrets, show unbelievable creativity.

Portal 2’s high points rival “the cake is a lie,” though they’re perhaps less quotable (which is honestly fine – repeating GLaDOS lines stopped being funny a long time ago). You’ll never forget the moments that accompany some of the achievements/trophies. The game’s quality stays consistently outstanding throughout; there isn’t a minute of filler content to be found anywhere in single-player or co-op. I would have loved to see something unique done with the story, which doesn’t end anywhere interesting despite a reasonably satisfying ending. I would adore seeing Portal stretch its wings beyond being a series of puzzles that almost always have one correct solution waiting to be found. That said, the next game I want to play is a second run through of Portal 2, because the existing formula is excellent and brilliantly executed.