The Orange Box was a quixotic endeavour: unusual and idealistic. It’s also probably the greatest value for money purchase in the history of gaming. But while the ongoing adventures of Gordon Freeman and Team Fortress 2 were the bulk, it was Portal that stole hearts. It was also whole, self-contained and neatly tied up, before success made a sequel inevitable.

Portal hasn’t been reinvented: it has been re-engineered to bear the weight of a much mightier structure.

The original’s three-hour running time gives way to separate and lengthy single player and co-op campaigns, complete with a celebrity voice cast and a major increase in explosive set pieces. Everything suggested by the original, Portal 2, enlarges and accelerates. Its puzzles are yet more adventurous and playful, and its script and world are granted much greater attention and detail.

The first hour reintroduces the portal gun efficiently while setting up your companion Wheatley (see ‘Personality core’) and the return of the sadistic AI matriarch GLaDOS.

The fundamentals remain the same. As the mysterious test subject Chell, you are forced to solve deadly puzzles, using a handheld device to paint linked interspatial portals on to surfaces, leaping through them to cross otherwise impassable gaps.

The game teases out expectations delightfully with a series of familiar-looking challenges before the first of many jack-in-the-box switches that throw Chell into a whole different game.

Portal 2’s difference is scale. Though you’re on a straight path through the (now partially destroyed) Aperture Science Laboratories, the locations this time around can be gigantic, showcasing abandoned facilities, scooped-out machine shafts and the innards of some mechanical monster. There are great moments which are not so much of discovery but of forehead-slapping realisation: Portal 2’s puzzles have you in a space for an hour, craning to see every nook and cranny, firing portals everywhere while only ever getting halfway to a solution.

Then one overlooked variable makes it all click.

The game’s logic is impeccable but its joy is all in the motion, as the answer hits and Chell fires from pillar to post like a rubber ball, it’s impossible to deny yourself a grin.

The major addition — gel that can be funnelled through portals and splattered on to surfaces — syncs neatly with the standard abilities. There are three gels: Orange speeds anything up that moves across it, Blue sends players and level furniture bouncing, and White can be slathered on previously portal-resistant surfaces to allow new purchase for your space-warping wormholes. The gels’ properties, with their gorgeously gooey physics, exaggerate and accelerate the chaos of the puzzles, adding super-speed highways between portals, setting up dizzying ricochet relays, or simply propelling you into vertiginous positions in anticipation of a bowel-loosening free fall. The potential for setting up huge rat runs is hinted at, before more expansive challenges really deliver: you trigger traps with a human cannonball, shooting away before they can close, feeling like a rocket and a rocket scientist simultaneously.

Portal’s mechanics make the jump smoothly: both players have a gun, though they can’t use them to link up each other’s portals, and both have to get to the exit to complete a level. There is a range of onscreen pointers and commands that help co-ordinate play, as well as a set of gestures — waving, hugging, and dancing — that incur the wrath of the on looking GLaDOS.

Only a few of the co-op puzzles truly stumped our crack team, but then the point that isn’t working out is what to do: it’s doing it in tandem.

This is where Portal 2 shows a genius for physical comedy by constantly putting each player’s life in the hands of the other, juggling responsibility between the team and letting someone drop the ball.

It always happens: misplacing a portal and shooting your partner into a spiked wall, pressing a button at the wrong time and watching them slowly fall into the abyss, or the classic: turning off the hard light bridge when they’re halfway across. When you get it right, there’s a sense of a shared achievement; when you get it wrong, it can be laugh-out-loud funny.

In both campaigns, Portal achieves a rare excellence: it’s a remarkably smooth ride that is always just the right side of demanding.

Usually a master of the wordless narrative, Valve here has decided to divide action and plot, setting the player only the most undemanding tasks while exposition occurs. Yes, it’s true: the most valorised of videogame storytellers may have made the single player so talkative that it very occasionally becomes dull.

Who cares? Portal 2 delivers, and it does it in style, creating one of the most meticulously designed, thrilling and delightful playgrounds we’ve ever seen. It’s a game with a magical take on momentum, where single bounds over tall buildings are business as usual, where every surface is a potential launch pad and the entire experience is a belly laugh.

Valve has a pretty good record with the number two, but attempting to inflate Portal’s perfectly formed package could easily have been a disaster. Naturally, the sequel doesn’t feel as bracingly fresh as the 2007 game but it’s precisely the sort of dizzying follow-up the original deserves.