Since sitting down to watch the first teaser trailers for Portal, we’ve been itching to get to grips with Valve’s latest baby. The humour and the immense puzzle potential alone got us hooked, so despite only being offered up as a four-hour ‘micro-game’ of sorts, Portal stoked our fire for The Orange Box more than even Gordon’s latest crab-clubbing escapade (and believe us, that’s saying something). It’s probably little surprise then that this was the first game we played seconds after being plonked down on a couch in Valve’s offices. Sure, the PR wanted us to focus on Half-Life 2 first and foremost and yes, we were scheduled to play the next day, but as soon as the door closed we picked it out of the menu and stuck two fingers up to convention (metaphorically, of course).

The game opens with the player stuck inside a small glass-walled cubicle replete with a bed, toilet and clock radio. When the female computer voice (as featured to amusing effect in the teaser trailers) speaks for the first time, you learn you’ve been detained, presumably for bad behaviour, in a kind of on-campus correctional facility. You’re in a place called the Aperture Science Enrichment Centre and you’re scheduled to undergo some training. It’s immediately clear that all’s not well, however. There’s no one around to meet you and the computer voice garbles occasionally as she directs you out of your pen, via a summoned portal, onto the first of a series of tests.

The mystery surrounding the game, and your part in it, isn’t given up lightly. In fact, Portal is something of an enigma right up to its conclusion. Valve has regularly hinted in numerous interviews that the game is part of the Half-Life universe, and that fact is initially made clear through a variation of audiovisual clues. Subtle sound effects lifted straight from Half-Life 2, for example, and graphical touches you can’t quite put your finger on. Obviously, the fact that the game is built using Valve’s proprietary Source engine plays its part, but there’s definitely a link and it’s up to you to find out what it is.

Before we look at the game proper, though, a thought should almost certainly be spared for the incredible work behind your only real companion in Portal: the computer voice. More than anything she’s funny; clearly as mad as a box of epileptic frogs, but funny all the same. Thanks to great scripting and the way events in the Enrichment Centre pan out, she’ll have you in stitches with deadpan lines like ‘thank you for helping us help you help us all’. However, it’s not long before you’re left biting your nails with utterings explaining that the penalty of failure in a given task includes ‘an unsatisfactory mark on your testing record – followed by death’. Towards the start she’ll follow up such remarks that lead you to believe she’s just testing your ability to perform under pressure, but given the fact that the computer is clearly malfunctioning, until you hit pay dirt a good two-thirds of the way through the game, you’re never quite sure where you are. Is it a simple test, or has the computer gone HAL 9000? Sorry, no spoilers from us…

So, portals then. You might think you know a thing or two about them having played Prey perhaps, but while the act of jumping through space time-holes is adequately covered, you’re by no means a real part of the proceedings, merely a traveller. Portal is different. Here, using the Aperture Science Handheld Portal Device (ASHPD) you can create entrance and exit portals in almost any space big enough to support them and must use them to negotiate a series of 19 progressively more difficult tests. Each test has an entrance and an exit – all you have to do is figure out how to get through them. Amusingly, the computer will often set out to explain the pieces of the puzzle as you enter each testing area, but thanks to cryptic wording and well-placed static interruptions, you never really glean enough to know quite what’s going on.

While the difficulty of the puzzles is curved to introduce you to the ASHPD as gently as possible, it’s not until the tenth test that you’re finally let loose with it proper (until then exit portals are placed for you). We’d probably be quicker to grumble had the difficulty been stacked the other way, but Valve was clearly concerned that some people wouldn’t get it, which in some ways is a shame.

Since it’s only a shade over three hours long (assuming you’re quick to grasp the concept) we had our reservations but, given the quality of the puzzles in the later levels and the remarkable way the story concludes, it’s not enough of a gripe to affect a topnotch score. Oh, one more thing: Portal has the best end credits ever…