"Left 4 Dead 2" may have featured four brand-new characters and all new environments, but fans still have a fondness for the original campaign chapters. "No Mercy" was already released as part of the last DLC pack, "The Sacrifice," and now the remaining three will be coming in the next pack. Also in the pack is a brand new campaign called "Cold Stream," which was actually created by the "Left 4 Dead" fan community.
Valve offered a few details about the upcoming DLC on its Left 4 Dead Blog. Modder Matthew Lourdelet, known among "L4D" fans for his work on the "2 Evil Eyes" campaign map, has been working on a new one called "Cold Stream." Valve gave "Cold Stream" a look and decided that it would go well with a planned DLC release of the original game's remaining campaigns. Lourdelet is still working to wrap up his work, but that's okay since the DLC is still a ways off.
While Valve's stance on giving a release date for the pack is the standard "when it's ready" line, the blog does note that we shouldn't expect to see anything until after the release of "Portal 2" in mid-April. There's no name for the pack yet, and no other details being revealed at this time. Though if the previous "No Mercy" release for "L4D2" is any indication, you can expect to see those original maps enhanced in the DLC by the addition of the sequel's new features: added weapons, a wider range of special zombies, new game modes and the like.