Portal Review

Waking in a small glass room at an unknown location, you're welcomed ("again") to the Aperture Science Enrichment Centre, a sequence of 19 scenarios designed to test your ability to use portals to bypass concrete walls, transport crates over impossible obstacles, slingshot yourself across chasms and overcome mischievous gun turrets. The first levels serve as a gentle introduction to the various concepts at work, and it's a good few minutes before you gain access to the weapon itself, and even longer before it's fully operational. Once it is, you can fire a blue portal at one surface and an orange portal at another, step through either and exit the other.

Levels demand a mixture of skills, all of which make use of portals in some way and your new tool when you acquire it. Some involve transporting crates to red switches in other areas of the test chamber; others, redirecting flying energy pellets to power up doors and platforms. The gun turrets, armoured on the sides and alarmingly powerful, represent a more dangerous obstacle, cutting you down if you stray into their sights for even a second, and need to be knocked over to disable them, or avoided altogether. Framing the gameplay are the portal placement restrictions - grey concrete floors, walls and ceilings can accept a portal, but reflective black sections, moving surfaces, doors, glass partitions and other world-objects cannot - and those springy metal rods tied to your calves, which allow you to fall over vast distances without incurring damage.

Who, or what, is behind these frosted windows? I wish I could tell you.

Most exciting are the sections that rely on momentum, which is conserved as you travel through portals. Place an entrance at ground level and an exit high up on a wall and step through the lower portal so that you're tumbling from a great height, and rather than simply land on the floor again you can reposition the entrance portal to catch you, which has the effect of throwing you out of the elevated portal a second time at terrific velocity. The implications ought to be obvious, and the puzzles that derive from this mechanic are some of the game's best and most spectacular, calling to mind the vehicular acrobatics of TrackMania.

Accompanying you on your journey and helping you to understand what's going on is the robotic voice of the AI that governs the test centre, GLaDOS - part instructor, part antagonist, total fruit-loop. While you learn, she keeps you amused, reminding you that any appearance of danger is "merely a device to enhance your testing experience", promising not to watch, then promising to stop lying about not watching you, and complimenting you on your intuition. "You remain resolute and resourceful in an atmosphere of extreme pessimism," she intones without emotion, before promising cake if you win.

The sentry guns demonstrate low levels of potential variety - confront, or dodge?

If you've spent as much time analysing the original Portal trailer as we have, you might wish GLaDOS would stop jabbering and let you have your fun, but this would be unwise, as the education you receive is important and cleverly articulated. One of the game's great strengths, if not its greatest, is that concepts are introduced in such a way that players are entertained and informed without exception or confusion, guided by subtle design decisions that emphasise particular elements and concepts by constraining your actions without ever actually seeming to. If another Gordon, Brown, is reading, we'd like to nominate Valve to take charge of Britain's education system. The people there could stand to start thinking with portals.

Yet despite a remarkable economy of design, Valve gets more out of the portal gun than it ever did out of gravity. It may only be one weapon, with you for the majority of the game, but it's easier to think of your growing portal expertise as a substitute for your traditional FPS arsenal. In your head, each scenario has you scrolling a mental mousewheel of abilities and tricks. Would this work here? What about that? As you apply their logic to the scenarios playing out in front of you, they slot into increasingly elaborate combination, and new ideas present themselves intuitively.

If you can get behind the guns, you can pick them up, at which point they start whining at you.

Taken out of context, screenshots of vast rooms, full of networked infrared sentry beams, floating platforms, angled walls and flying energy pellets appear overwhelming; in the context of the game they are simply fascinating challenges that you are well equipped to overcome. It's rewarding, not frustrating, to sit and ponder one, partly because of that economy of design, partly because the pacing is so patiently considered, and partly because it always comes together with such delightful eloquence. And, of course, partly because GLaDOS is always there with something to say.

GLaDOS does more than simply guide you, however - she is the heart and soul of Portal's biggest surprise. Know simply that Valve harnesses its strengths in storytelling to drive your fascination with the Enrichment Centre - as wonderfully realised a location as anywhere in Half-Life - and with GlaDOS.

As the game reaches its apex, the scripted feel of the earlier levels is ousted in favour of something closer to a Half-Life episode. Its conclusion is funny, original and extremely memorable, as you dismantle the game's very personality and achieve a manner of revenge. Gabe Newell was right when he said it was Valve's best to date.

As a component part of an admirably vast whole, Orange Box, Portal gets away with its brevity - first-time completion rates of less than three hours will be the norm for FPS devotees - and in doing so comes close to that increasingly likely gaming future: single-sitting, film-length entertainment experiences. It's closer to the episodic ideal than Valve's own Half-Life episodes have proven thus far. Beyond the main narrative single-player mode, you're invited to gun for achievements - certainly present in the PC and 360 builds, both of which we've completed - and tackle advanced levels and 'challenge' versions.

'Advanced' tours through the latter six test chamber scenarios with seemingly vital elements removed, or conditions skewed to enhance the difficulty. The Weighted Cube becomes a bouncy ball, while other solutions, dependent on the flinging concept, do away with charitable portal surfaces, forcing you to leverage every second of a pliable surface's exposure, laying down exits during feats of acrobatics with the precision of a traditional twitch-killer. One of the best advanced levels is the adaptation of a mid-game scenario built primarily around sentry guns, this time encasing them in indestructible cages, forcing you to build your strategy around evasion rather than confrontation for the second attempt. More of this, in the form of downloadable content, will be welcome.

All hail the Companion Cube!

Elsewhere, 'Challenge' mode imposes other conditions - using the fewest number of portals, the least possible number of steps (effectively the opposite of the least-portals goal), or achieving the solution in the shortest amount of time. More than simply space-fillers, the challenge levels help drive you toward new patterns of play, revisiting levels with a view to reduce them to the purest, simplest solution. You'll tear your hair out in places, but bending the rules of the already thoroughly bent portal gun rulebook is worth the aggravation.

Beyond that, it should be said, there is almost nothing frustrating or poorly conceived in Portal's design - an astonishing achievement given the degree to which the portal gun reshapes the movement potential of a player. Listening to the (once again extremely revealing) developer commentary, with contributions from developers like Kim Swift, Robin Walker and even GLaDOS actress Ellen McLain, the degree to which tester feedback informed level design, and the level of purpose invested in every nook, crate and glass partition, is laid bare.

There's common sense (portals never kill you - if you're in one and it closes, you're simply pushed back into the world) as well as uncommon sense (observation rooms represented as frosted glass windows with desks and chairs behind them are not just a G-Man-style narrative indulgence - they give Valve another light source to play with, allowing them to direct your attention to certain areas) and pleasant inferences to draw (the GLaDOS humour is often used at junctions where it's necessary to keep you still long enough to witness something instructive). At times, it's as fascinating to observe Valve's attention to detail in action, as it is satisfying to nail the solution to a puzzle.

As the game nears completion, we get some of the best chambers. This, on Advanced, is riveting.

Nevertheless, it's hard not to return to the fact that it's all over so soon, and, with so few puzzles actually to tackle once you're in your stride, not feel slightly let down. Some of the better concepts - using portals to manipulate rockets fired by sentry turrets into offensive weapons - are scarcely used, and the vaunted link between Aperture Science and the world of the Half-Life games is less dramatic than we had hoped.