I created a set of house rules to play Doom in a slightly different way.  I call it Doom: Assault Team and it is a quicker, force-on-force style of play that is not as difficult or time intensive as using the basic rules.  Though most of the basic rules are used, I changed how the game is set-up and I made some changes to the marine turn and invader turn.  I play-tested it thoroughly, and it actually works quite well.  I sometimes just pulled randoam map board pieces out of the box and made a completely random map, and the game played fine using a set-up like this.  Hopefully this will help to prevent a lot of pre-planning before playing Doom...using these rules, you can just open the box(s), set-up a random board, and start playing.  However, I also designed various sample missions (included with the rules on my Photobucket page) that can be linked in a campaign or used to send your assault teams on special missions.  I posted the rules on my Photobucket page.  Just click on the link below, and then look at "Sub-albums" on the right side of the page.  You'll see an album titled "Doom: Assault Team."  Click on this album to open it and look at the 13-pages of rules I downloaded for the mod.  Actually, there are really only about two pages of rules.  There are three pages of charts to be used with the mod, and the rest is mission descriptions for different types of missions you can send your assault teams on.  While you're on my photobucket page, check out my painted miniatures and other Doom missions I have uploaded (such as "Congo" in the "Doom Missions" sub-folder and my massive, 36-page "Jupiter Rising Campaign" in the "Jupiter Rising" Sub-folder). 

http://s337.photobucket.com/albums/n400/BarbarianWanderer/

Here's a direct link to my photobucket page where you can view and/or print the instructions for Doom: Assault Team.  Let me know what you think.

http://s337.photobucket.com/albums/n400/BarbarianWanderer/