First, the bad news. Valve has apparently brought the Portal alternate reality game, which kicked off recently after a sneaky update to the game, to a close.

Good news? They've done it by confirming Portal 2 for release this year.

Specifically, the initial updates indicate that Portal 2 - which probably carries on directly from the new, extended ending of the original game - will be out in time for Christmas 2010. It's coming to PC and Xbox 360, as you'd expect, and a number of retailers are already taking pre-orders.

Portal 2 will apparently not come with Episode 3 or any other games, as the first Portal came with Episode 2 and Team Fortress 2. It'll be it's own, big standalone release, at full price.

Portal 2 will take the series in a slightly different direction too, with a new Game Informer article promising "new gameplay mechanics, storyline, and some surprising new twists."

One of those new features will apparently be co-op gameplay, with the finale to Valve's latest ARG finishing with the words "Cooperative Trial Completed", before saying that "You will be contacted when the live first phase of the Cooperative Testing Initiative is ready to accept applicants."

Story details have been leaked by retailers (Spoiler alert), which reveal that players will explore new areas of Aperture Science and be introduced to two new characters in a separate co-op campaign. The new characters will be bi-pedal robots - one an enhanced Turret, the other a mobile GlaDOS unit. Co-op will work online and locally, with new weapons such as a tractor beam being worked into the feature-list.

The singleplayer campaign will take place hundreds of years after the first game, but will still star Chell. Aperture Labs has been ravaged and overgrown in the time between the two titles.

Physical properties can now be merged through portals to allow you to customise an area too. Special paints appear in the labs which will give speed boosts or more friction to players, so positioning these is pivotal to the new puzzles.

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