Even if you have a killer video game that's flying off both the physical and digital shelves, it never hurts to throw some freebies to the players who love it.

On October 4, Valve released the first free downloadable content pack for Portal 2. The additional content, which streams in as an update to the Mac OS X steam client, comes in at over one gigabyte in size and includes both single player and cooperative challenge modes as well as a slew of unlockable levels and challenges to feed your Portal 2 obsession. While similar to standard Portal 2 gameplay, the challenge mode puzzles will push you to complete a test chamber under specific time, movement or portal restrictions. Valve also occasionally added its own nigh-demonic elements (such as turrets, lava, pitfalls, random obstacles, and more) to each room. 

Perhaps the most interesting chunk of the downloadable content pack is the continuation of Portal 2's co-op mode. The additional content (referred to in the game as "Peer Review") offers an entirely new campaign for Atlas and P-Body, the two test robots that must work together to progress through the test rooms and survive in one piece. With the expansion, their story continues, and even if you do wind up dying and being regenerated/rebuilt time and time again, it's an entirely new playground to run around on as well as new puzzles to go half mad solving and the joy of victory hitting you after you've figured out the thing that was driving you and a friend nuts for the past several minutes.

While there's been some criticism as to the timing of the Portal 2 downloadable content pack (some said it arrived a bit late to the party, while others argue that Valve releases content when it feels comfortable with it), this is still additional content and additional game hours for free and delivered fairly automatically to your door with no extra steps. All you have to do is sit back, let the update happen and the new content is there the next time you launch the game -- which is never a bad thing.

Portal 2 retails for $29.99 and requires a 2 GHz or faster Intel-based Mac running Mac OS X 10.6.7 or later.

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Portal 2 DLC Gallery

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  Cooperation will be a necessity in the new "Peer Review" co-op levels of Portal 2's downloadable content update.

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  Grab the items you need, even if you need to yank them through an external dimension...

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  Atlas and P-Body face additional challenges in brand new Portal 2 levels.

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  Propulsion Gel: It's blue, it's weird and it's amazingly useful.

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  The boys are back...and so is your local, evil, raving supercomputer villain.

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  Yes, the new levels will be dangerous, frightening and full of things that can destroy you. It builds character.

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  Have a portal gun and a friend? Then it's time for the new levels.

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  With a portal, you and your friends have a door to almost anywhere.

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  It's called teamwork...and sometime's it's painful.

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  Mistakes may have been made. That's why the game will happily rebuild your destroyed 'bot and give you yet another chance...

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