Screenshots and additional info here → http://imgur.com/a/fdrrw
Snapmap Code → http://imgur.com/a/fdrrw
It's a pretty standard Doom experience. I've based the first part of the level's layout on the first level from Doom 2, and spent a fair amount of time trying to get the logic to work to support either solo play or up to four player co-op (haven't tested it yet, so apologies if the logic breaks down - especially in the end-zone lockdown - with more than one player).
There's a nasty little secret in there to be found too, but I think it's worth the pain to find it.