A first look at Valve's Portal 2

The sequel to Valve's smash hit Portal, which you may be surprised to hear is called Portal 2, is finally out - and if you want to know why our first look at the title is a day late, read on.

The original Portal was released as part of the company's Orange Box compilation - which also included Half Life 2, Episode One, Episode Two, and Team Fortress 2 - as the spiritual successor to the indie freeware title Narbacular Drop, after its developers were snapped up by Valve to become full-time employees.

While short, the addictive gameplay - which saw players take control of Chell, held prisoner by a deranged AI and forced to solve deadly puzzles using a gun which generates linked portals - and the great character of the antagonist GLaDOS saw the game receive critical acclaim. Although detractors often refer to the title as the 'box-carrying game,' Portal's blend of physics-based puzzle solving and first-person platforming action ensured it gained a cult following.

That following has been eagerly awaiting the release of Portal 2, which sees the return of neurotoxin-loving AI GLaDOS, along with the introduction of helpful - if dim - sphere Wheatley, played by comedian Stephen Merchant. The release has been so anticipated that fans have spent hundreds of hours solving a fiendish alternate reality game devised by Valve in order to to push the release date of the PC version forward by a couple of days - but was it worth it?

It's hard to offer a first look at Portal 2 without giving too much of the plot away - but we'll try. Set an unspecified amount of time after the first game, the clean lines of the Aperture Science Enrichment Centre have been worn away by the ravages of age and nature - and those who found the first game too sterile will be impressed with the detail and richness of the environments this time around.

The environment is significantly bigger in the sequel, too - and a lot more varied. The facility feels a lot more realistic, if on a scale far too grand to be true, and some of the graphical effects are breathtaking - even on the Xbox 360 and PlayStation 3 versions, which suffer from lower-quality visuals compared to the PC and Mac releases.

The Enrichment Centre's growth isn't just for show, though - while the original title largely got away with being a short romp thanks to its inclusion in a collection with several other games, Portal 2 is a standalone title - and Valve has worked hard to make it feel worth the entry fee. The single-player campaign is at least twice as long as the original, while a new co-operative campaign of equal size - which sees a pair of players take control of a pair of robots each armed with its own portal gun - puts the game at over four times the size of the original, at conservative estimates.

If the game used the same puzzle mechanics of the original, it would be easy for gamers to get bored - but Valve's thought of that too. The introduction of Aerial Faith Plates, Repulsion Gel - Aperture Science's first and last attempt at creating a diet-friendly pudding substitute, which bounces off stomach linings and back out of the mouth before calories can be consumed - and other new mechanics keep things feeling fresh, while being introduced at a pace that means the player is rarely left feeling overwhelmed or confused.

Now, at the start we promised that we'd explain why this first look article didn't appear yesterday, when the game was officially released in the UK - and we shall. Sitting down to play the Xbox 360 version yesterday, the addictive nature of the gameplay and the excellent storytelling - something that Valve has a great handle on - left us begging for 'just one more go,' until the single player campaign was finished and our families were filing missing persons reports.

Those who disliked the very principles of the original will likely find little in Portal 2 to convince them to change their minds, but if your complaint revolves around sterile environments, repetitive puzzles, or a lack of interaction with the game's antagonist, Portal 2 comes highly recommended - and if you're a fan of the original, the chances are you've already bought it.

Valve's Portal 2 is out now on Xbox 360, PlayStation 3, PC, and Mac.