It wasn't long ago that Valve asked the community for awesome mods for the four player co-op game Left 4 Dead 2. Today, we get that answer. A user mod containing new campaign levels is being released called Cold Stream, the focus is an outdoors type area set in the daylight and filled with plenty of zombies to kill.
The mod is in beta though and Valve is asking the community to give the campaign a playthrough and report any bugs back, this is done through the in-game bug reporter. According to Valve you can expect missing art assets, improper hit boxes, and possible navigation issues. Still - from what we've played of the beta - this is a pretty polished (and fun) little mod.
To download it make sure you opt into beta on Steam and it should be automatically download into your Left 4 Dead 2 game.