As we reported yesterday, Valve has revealed the first details about the downloadable content for the FPS puzzle game, Portal 2. The add-on is in development as we speak and is set for a Summer 2011 release.

The developers promised new test chambers for players, leaderboards, challenge mode for single and multiplayer modes and more. The best part is that the Portal 2 DLC is free and will be available for PC, Mac, Xbox 360 and PS3.

The game is getting top honors from various publications (including us, of course) and is currently the best-selling title in UK, Germany and the Nordic countries during its first week of availability, which makes it the fastest-selling Valve release since Half-Life 2.

This is good news, especially the 'being free' part. Valve knows how to keep its community happy.