The recently unveiled Left 4 Dead Survival pack for the Xbox 360 and PC will be free, Valve announced today.
The pack, due this spring, introduces a new multiplayer game mode entitled, Survival, plus two complete campaigns for Versus Mode (Death Toll, Dead Air). A Critic's Choice Edition of the game will be heading to retail stores this spring, and will include access to all the content introduced in the L4D: Survival Pack.
Well played, Valve. Well played.
Check this out for a full run down of the pack.