Left 4 Dead Intro
The cinematic was developed over about three and a half months and sets the stage for a rather depressing, but exciting, zombie apocalypse. In addition to being well designed, animated, and edited, this intro cinematic weaves some important gameplay lessons into the story. For instance, when Louis leaves the group in an attempt to hail the helicopter, the others have to come save him from death. Likewise, in the game it is never wise to split up.
The cinematic delivers story, emotion, and generally prepares players for the setting in which the game takes place. In an insightful blog post about the development of the intro cinematic, Jason Mitchell (Valve) writes:
Because Left 4 Dead is a new property for us, we wanted to provide some basic player training prior to the start of the game. Traditional in-game training mechanics didn't make sense for Left 4 Dead, because they would take away from the sense that players had been immediately dropped into a very real, very dire zombie apocalypse. We didn't want a slow ramp-up in gameplay to take away from that tension. As a result, we decided that it would make sense to begin the game experience with a non-interactive introductory movie that could get players revved up and subtly cue them to important gameplay mechanics such as "light disturbs the witch" and "car alarms attract the horde."
The intro cinematic went through a number of iterations, as all cinematics do. Interestingly, however, the initial blockout was done using in-engine tools which gave it a distinct machinima feel. In Jason Mitchell’s blog post, he shared videos of its development at key points:

Work in Progress - July 8, 2008
Work in Progress - July 25, 2008
Work in Progress - September 4, 2008
Further Learning
The Moviemaking Process: Left 4 Dead's Intro Movie (Blog Post)
Cinematic Credits
Editor: Lars Jensvold
Music Editor (Cinematic): Eric Holland

Credit list not complete. Confirmed credits only. If you worked on this cinematic, or know someone who did, please let us know at info@behindthecinematic.com or by sending us a message on Twitter.
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