Valve plans to repeat the quick sequel process used with the release of Left 4 Dead 2.
On the heels of Valve's previous "three surprises" announcement, company boss Gabe Newell said that another quick-release sequel--as seen with the surprisingly fast outing of Left 4 Dead 2--will be released "at some point." He added that Valve learned a lesson with L4D2 in that it was a surprise to customers, and that there's a certain amount of entertainment value in that kind of quick release.
He also hinted to the backlash Valve received shortly after L4D2's launch. Fans of the original game claimed that there wasn't enough time to develop a true sequel, and insinuated that the resulting product was nothing more than a glorified expansion pack. The opinion seemingly changed over time as the game proved to be an outstanding sequel, receiving strong positive reviews.
"There's also a certain amount of fear value in that," Newell said, referring to a quick sequel process, "because the traditional surprise in the gaming industry is not 'Oh, I’m surprised: something good happened!' The traditional surprise is 'Oh, I’m surprised: X-Fire just got bought again and went away.' 'Oh, I’m surprised because something horrible has happened to a franchise that I’ve been following since I was a little kid.'"
Naturally Newell didn't drop any hints as to the next quick sequel, however it could easily fall into the company's planned "big three surprises" slated to be announced over the next twelve months. Speculated "big three" titles include Half-Life 3, Half-Life 2: Episode 3, and Portal 3.