There's a post by Gabe Newell on Edge Online offering the Valve Managing Director's pleased reaction to this week's release of Left 4 Dead. He offers some fascinating insights into the process they've created for developing and testing games, describing behavioral modeling they do to determine the comfort level of players in their games, and describing the way this enables them to create a proper sense of pace. He offers insights on one of their "theories of fun," challenges they overcame, and the emphasis they place on testing, testing, and more testing. Also, the Left 4 Dead live interview on Eurogamer transcribes a live chat with Valve's Chet Faliszek from earlier today. Along the way Chet explains the game's long development cycle: "That is a common question for people who played it back awhile back. While many of the core mechanics remain the same - the focus on co-op from the ground up etc., many of the polish and tweaking levels still remained. And when Valve was able to supplement the original team of 10 with a team of 50, we were able to give it a complete graphical overhaul as well. And that wasn't just to look pretty, but served gameplay elements as well."