Tripwire user Marco has been quietly constructing a Doom 1 and 2 Mod and released an initial pack for the community to enjoy.
The thread, instructions, and download links can be found here (//http://forums.tripwireinteractive.com/showthread.php?t=36983).
A few images to give you an idea of how it looks and feels in game.
(//http://i683.photobucket.com/albums/vv191/arramus/Killing%20Floor/doom1and2.jpg)
(//http://i683.photobucket.com/albums/vv191/arramus/Killing%20Floor/fire.jpg)
(//http://i683.photobucket.com/albums/vv191/arramus/Killing%20Floor/beast.jpg)
(//http://i683.photobucket.com/albums/vv191/arramus/Killing%20Floor/doomgun.jpg)
There are a few bugs to resolve. namely; targetting and server stability. There are also a few other features that would make it a better experience like respawn without having to leave the server but it's looking and playing well.