I've owned it for a while now. Much like Space Crusade is the little brother to Space Hulk and HeroQuest is the elder version of Descent, Doom is the newest reincarnation of Aliens with a little SotC thrown in for good measure. I love Doom. As a matter of fact, I've been off and on in a BGG forum concerning Doom all day!
Did you get the expansion? New monsters and Marines, extra terrain and scenarios, as well as marine vs marine deathmatch rules. It rocketh mightily!