Portal 2 sees the long awaited return of GLaDOS and Chell for more mind-bending physics puzzles.

The original was set in a clinical, pristine Aperture Science facility, but in Portal 2 this place has fallen into disrepair. Set hundreds of years after the end of the first game, the heroine Chell awakes to find herself in a research facility that's overgrown and dilapidated. A robot 'personality sphere' meets Chell to help her, but in the process wakes up GLaDOS. She is not happy to see Chell, and so a series of deadly 'tests' begins again.

On PC and Mac Portal 2 looks great, with rich detailed environments and excellent animation. While the original's story was only really hinted at, here it is fleshed out and you will learn a lot about Aperture Science and the characters in the game. While Chell remains silent, GLaDOS and the personality sphere Wheatley are full of character and are both hilarious and terrifying.

Portal 2's puzzles are excellent. The Aperture Science Handheld Portal Device returns and works as normal, but there are many additions to the original's set of tools and traps: there are Pneumatic Diversity Vents, Propulsion and Repulsion Gels, Thermal Discouragement laser beams, Aerial Faith Plates and more. The increased length and expanded story mean Portal 2 is unlikely to be as iconic as the first, but the single player campaign is a fantastic ride, and once it's over there is another excellent series of two player cooperative tests to undertake with two excellently animated robots.

With its mix of puzzles, action and menacing humor, Portal 2 is one of the games of 2011.