Another one of those fantastic shipboard scenarios, Dark Blood starts off with the survivors leaving their smalll dingy to an oil tanker. Aboard the oil tanker, you just basically shoot zombies. Highly detailed, and with enough directions to get you through the map, Dark Blood is a testament to how much better mappers are these days.
An unarguable 91/100
Map by CastorJudo, downloadable here at www.l4dmaps.com
While you're there, sign up in the forums and participate in relatively civilized conversations regarding L4D and practically everything else.