Among the additions of making Death Toll and Dead Air available for versus play, the 'Survival' mode seems to be getting the most attention - and for good reason. Valve seems to be trying to seperate the "men from the boys", for lack of a better analogy. Officially announced additions for the DLC include: [*:3ez62kin]Death Toll and Dead Air for versus play; [*:3ez62kin]Support for the Source SDK and custom works by fans; [*:3ez62kin]Survival mode in 16 maps based on the current campaigns, and Lighthouse - a new map for this mode; [*:3ez62kin]New lines of dialogue but no new weaponry; [*:3ez62kin]New achievements for PC users (assumingly, as they stated there would be "no new achievements for 360 users" but did not mention PC users); The survival mode, as you can see from the videos here contains a timer recording how long your team is able to withstand the onslaught of the horde - but it's not that simple. According to comments when the DLC was revealed, you could encounter three smokers and a boomer, or even multiple tanks; and as has been seen in the videos on IGN, the hordes can trigger while you're attempting to fight off a tank. The new mode sounds like tons of fun for those whom are tired of the predictability of the campaigns and wish to extend their interest in the game. I can't wait to see what additions they add which haven't been mentioned.