You like killing zombies, right? Dumb question. Of course you do! This is a no-brainer then. Valve has offered to unlock Left 4 Dead campaign "Dead Air" early, on July 22, before the rest of the original game's campaigns are released as part of the Left 4 Dead 2 DLC, "Cold Stream." There's a catch though: you have to play Left 4 Dead 2.
No, seriously. Dead Air will unlock once 20,000 players complete the currently-in-beta Cold Stream campaign and earn the Stream Crosser achievement on Steam, Valve
confirms. The DLC's titular campaign is a player-created effort and it has been available for download in beta form since late March. The early Dead Air unlock will only happen if this challenge is completed by Sunday, July 10.
Hey, look at that! L4D2 is on sale for $4.99 right now on Steam! What lucky timing!