Left 4 Dead has stood the test of time, more or less—and while there hasn't been a peep from the series in years, that's more down to Valve weirdness rather than a sign of a lack of interest from players. Half-Life was galactically successful, and we're all still waiting on a third game. Someday, Gabe, someday.
Part of Left 4 Dead's success was down to how straightforwardly good it was. You rock up, shoot zombies, and spam "pills here!" at every opportunity. There aren't classes or progression trees—and while a lot of those bells and whistles weren't common in the genre when it came out, it still made the game more accessible and focused. It's also why people are still playing it.
