Pretty cool. =)
This would actually make a really interesting flash game. Sort of an RPG version of L4D.
The way I see it, it wouldn't be too hard. Have the 4 campaigns, each with 5 fairly short chapters. As the player is going through, they have to beat the various randomized (and turn-based) zombie attacks and beat the campaign with at least one Survivor. Let the player find different weapons (marked by, I dunno, a skull or something on the screen), and they can "teach" these attacks and tools to their Survivors. With the new wave of items in L4D2, it'd be a fairly detailed game in and of itself. And might I add a very auspicious flash production.
But those are just thoughts. All in all, this was an entertaining animation with a fairly clever and original premise. The audio was spot-on and the art was humorous while catching the general style of the various characters. Use of the AI Director as a Rival figure was (while a relatively obvious move in hindsight) brilliant. In a way, this may be one of the best crossovers for a flash I've ever seen. Again, CLEVER. =)
Kudos.