Left 4 Dead: The Survival Pack Press kit
First off, you can now play the two campaigns Death Toll and Dead Air online in Versus mode. These maps have been tweaked slightly to remove some closets and to balance gameplay. For example, downstairs in the Boathouse Finale has been significantly emptied to prevent corner camping, and more walls break open.
The anticipated Survival Mode is released, which pits The Survivors against endless waves of the horde, as well as multiple Special Infected. Players can hold out in 16 maps, 15 of which are extracts from Crescendo Events and finales from the four original campaigns. These maps have also been tweaked to remove exploits and to make the whole experience much harder. The last map is in the new campaign: The Last Stand, and currently has one map: The Lighthouse.