Left 4 Dead 2, the co-operative zombie shooter from Valve, which many PC gamers feel to be one of the top games of the year, has announced its first pack of downloadable content - titled "The Passing".

There's not loads in the way of details yet - but we do know that the old survivors from Left 4 Dead - Bill, Louis, Zoey and Francis - will be making an appearance. More specifically, there'll be "a meeting" with the cast of L4D2. It'll be set in a small town in rural Georgia and be a completely new co-op campaign.

On top of that, there'll be new arenas for Survival, Scavenge and Versus modes, a new co-op challenge mode of play, a new zombie class, a melee weapon and a firearm. Finally, there'll be 10 new achievements to collect for the title, both on Steam and on the Xbox 360.

There's no pricing announced yet, and there's no release date more specific than early 2010. What we do have, though, is a quote from Valve's Doug Lombardi. He says: "The Passing will become the most important campaign in the Left 4 Dead story, as all the Survivors are being called together in one campaign".

We'll bring you more as we get it.