Edge has an extensive and rather interesting look back at the development of Left 4 Dead that touches on design philosophy and how people behave while playing.
"Some people would declare themselves the leader and bark instructions, whether they were qualified to or not," said Mike Booth, then CEO of Turtle Rock Studios, where the game originally began development. "Other guys just wanted to help out and make sure everyone had health kits. A few would just wait for the moment to stab you in the back." Other interesting anecdotes include a foursome who decided to just end it all by jumping off the rooftop at the opening of "No Mercy," and the Counter-Strike veterans who protected a gaming-illiterate father.
The article also looks at how Turtle Rock and Valve initially got together, the technology that produces the 30 zombies populating the game world at any given time and, our personal favorite, the evolution of Louis from "a religious nutjob" to the likeable office worker based on Faliszek and Wolpaw's pal from Cleveland. "I remember helping him move house," said Faliszek. "He dropped something, ruined it and still made a joke about it. That's the perfect guy you want in the zombie apocalypse." Who else is going to help you find all those pipe bombs?