Remember those bus ads for Portal 2? You can’t have missed them; Portal 2 posters covered everything that moved, and anything that didn’t, about three weeks ago.

Now, the dust has settled and the game has been played. And completed. So, can this first-person puzzler meet the hype?

Portal 2 had to be a brilliant sequel, probably the greatest sequel of all time, and, for the most part, it is. Well, if you take the strengths of Portal and amplify them the, yes, you have Portal 2.

Following on from the first, Portal 2 lands you right back in the sinister, soulless heart of Aperture Laboratories; a huge, far reaching new-technology company, obsessed with science and operators of questionable moral values where humans are concerned.

To mention the plot would ruin £40 worth of game. Needless to say, you are once again a human in a gargantuan testing facility at the mercy of a vindictive, science-junkie artificial intelligence, testing your way to freedom.

It’s a fan’s sequel from the get-go. You don’t need to have played Portal but if you haven’t you’ll feel like Billy No-Mates sitting in the corner of the room while everyone else shares a brilliant private joke, bonding them for life.

Happily, it works better as a sequel; expanding characters and fleshing out the world, as well as the gameplay. Slightly. Be warned; Portal 2 is every bit as psychologically worrying as its predecessor. This is truly brilliant narrative. Make no mistake.

You see, while Portal 2 is a joy to play; the story works in a perpetual scientific testing environment with a sinister beauty. It’s a worrying game, death is round every corner but, more frightening than that, is the fear of failure. Not because co-creator of The Office and Extras, Steve Merchant as the voice of a helpful robot, might pop up and irritate you, or make you laugh, but because the portal gun is fun. Man, that thing, it never gets old.

Popping out of one hole to fling yourself through another, it’s great. Then, add goop which can make you jump high, speed like a demon or help you place a portal wherever you like and Portal, once again, proves how compelling gaming can be. Each puzzle room is an addictive challenge, reminiscent of The Crystal Maze, with an equally irritating guide. “Just one more room”, people will say. Hours go by.

Hours and hours. And then? Well, then it ends. Portal 2 is woefully short. Portal was a short game, packed into a release containing four much larger, longer-developed games. It was meant to be completed in four or five hours. Portal 2 took this thumb bandit around 10 hours, over the course of a few days.

Oh, but there’s a two-player mode! Yes. Yes there is. It has to be, easily, the most compelling two-player (co-op) game I’ve ever played. You play as two robot-buddies, taking endless joy from endless portal testing. It’s all about team work; from success to failure. Portal 2 can be enjoyed with your folks, your girlfriend (or your boyfriend, if you’re bucking trends), with game-haters.

There are no death matches, no rocket launchers, no jeeps and no aliens; there’s co-operation, trial and error and proper bonding experiences. Play it with a friend, your friendship will reach a new zen you never knew could exist.

Still, around 25 co-op rooms later (and they do go fast when it’s this much fun) and Portal 2 is well and truly done.

This is why Portal 2 fails. It’s not worth £40; it’s nowhere near a full-priced video game, with all its extras, different modes, online options, multiplayer options, free downloads and the like. Portal 2 has two modes, a clunky menu system and a disastrous online search facility.

You need to be warned now, about Valve, makers of Portal 2. The same folks made Left 4 Dead, Left 4 Dead 2, Half Life 2 and its two other episodes, Team Fortress 2 and one or two others. Here’s the thing; all Valve games feel the same. The company uses the same game engines to build its titles – each game released feels like a mode which could be incorporated into the previous one. Left 4 Dead 2 had exactly the same problem.

From the simple, once eerie, title screens (featuring nothing but game title and a couple of options) to the terrain, walls, fog effects and that soullessness Valve does so well. On purpose or not. Like its sister games, Portal 2 drips with under energised potential.

There will eventually be downloadable additions to Portal 2, obviously. Valve will release new puzzle rooms, maybe even a new playing mode (one can hope), its already announced. But if Valve tries to charge for any of it, the company deserves to suffer – financial uncertainty, perhaps, maybe a heavy patent law suit, a punch on the nose. Something. If you’ve already paid £40 for Portal 2, you’ve already paid for all of its downloadable content.

It’s a big issue, value for money in gaming. Halo Reach, for example, is a fun fair compared to Portal 2’s bouncy castle in the back garden. But, arrgh! Portal 2 is just so damn good. It’s a great video game; a brilliant fuse of storytelling and gameplay, a true example of gaming as art and as an evolution in entertainment.

You must play it.

Portal 2 is available now on Xbox 360, PlayStation 3 and PC. RRP £40.