Destructoid: "If you paid attention to all the X10 news that broke out yesterday, you'd notice Left 4 Dead (both of them!) is receiving all sorts of new updates. Between a comic book, an awesome-sounding return to the original game with new downloadable content, and "The Passing" for Left 4 Dead 2, there is a ton of Left 4 Dead content coming out by April.
From all of my talking with Valve representatives, expect Left 4 Dead to live on in this manner, with DLC and patches. I can confirm that Left 4 Dead 3 will not be announced at all this year, for which fans of online petitions are surely disappointed. Anyhow, I was a lucky enough duck to play through the second chapter of Left 4 Dead 2 DLC "The Passing," called "Underground." It's a dark area, and while I didn't see the return of the old crew, I got some nice hands on with what we can expect next month."