Mind-bending puzzler Portal's come a long way since it was bundled alongside Valve Software's more eminent titles in 2007's The Orange Box. An instant hit, it received slavering praise for its ingenuity, deadpan robot humour and ability, like a good teacher, to make you feel smart. At the time, it was the only game FHM owned that merited an extended stay in the console despite the fact it didn’t involve killing people, zombies or aliens. And wasn’t called FIFA.

Aperture Laboratories have changed a bit since we last saw them.

However, as good as Portal was, it did have its issues: samey visuals, occasional lack of atmosphere and too few of the ‘wow’ moments that we’ve come to expect from big money productions. With the sequal earning its place as a stand-alone title, Portal retains much of the same gameplay. You have to 'shoot' portals that will zap you to otherwise unreachable parts of a series of tricksy rooms - but the graphics are improved and Stephen Merchant's been brought in to voice your chirpy robot guide. 

The sequel takes place some several hundred years after the original story, in the very same labs that main-character Chell managed to navigate her way out of. However, since the conclusion of the first game, the Aperture facility has been left completely abandoned, and has somewhat conveniently been ravished by nature. The labs are now full of collapsed walls, crumbling fixtures and loads of pesky vines and shrubbery which will no doubt make the labs far trickier to navigate than before, but also add a lot of colour to the previously clinical surroundings of Aperture.

These fellas are your guides. Their sexuality is unconfirmed.

The level design is inspired, with new puzzle tools including funnels, springboards, vaccuum tubes and special gels that can change an otherwise unremarkable wall into a trampoline, or a floor into a whizzy 'Slip' 'n 'Slide'. Oh, and murderous little laser beams can be twiddled this way and that with mirrored cubes.

The sequel's grown in size and profile, but the quirky creepiness lingers and the puzzles still strike the perfect balance between intricacy and inspiration. However, the fact that you can now play the game co-operatively, both locally and online, might be the achievement most worth marvelling at.

Portal 2 is out on PC, Mac, PS3 and Xbox 360 on April 21