I've been working on this a bit as a side project to see if I could recreate Dungeon Keeper in Source Engine and thought it would nice to post it here:
http://www.youtube.com/watch?v=tuxENY-KTYs
I think I got the most important basics working so far. I'm not really sure what direction to go with it yet. I could either try to recreate dungeon keeper as close as possible (but would need assets for it) or maybe go for an "Alien Swarm" style dk derived game (which should provide a nice number of creatures/aliens to populate the dungeon).