Valve is legendary for its sprawling development cycles and serial delays, so much so that the company's public development wiki has an entry for so-called "Valve Time." It's one of the side effects of the company's production mentality, which eschews top-down management in favor of team-driven initiative.
In reality, the Seattle-area developer has largely left behind its legacy of releasing a single game once in a blue moon. Since 2007, the studio has released at least one game per year, including the new franchises Left 4 Dead and Portal, the long-awated sequel Team Fortress 2, and the latest entry in the Half-Life 2 sub-series of now-regrettably-named "episodes."
But Valve writer Chet Faliszek, whose current project is "The Passing" DLC for Left 4 Dead 2, says this newer, more prolific Valve hasn't appeared in spite of the company's traditional self-driven practices -- it has developed because of them.