Official support for community created campaigns has just been added to Left 4 Dead , thanks to the most recent update to the game. Valve has also updated the Left 4 Dead authoring tools—so get crackin’ map makers! Valve announced the long-awaited PC version update via the official Left 4 Dead blog last week, highlighting the changes that will enable support for add-on campaigns. In effect, it means more widespread access to fresh campaigns beyond the original four—No Mercy, Death Toll, Dead Air and Blood Harvest—thanks

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Left 4 Dead Now Officially Supports Custom Campaigns [Valve]