fun fact: There was a doom book, actually four of them and the last two came out before the third game was made. (the one between "hell on earth" and "final doom" I think it was called "thy flesh consumed)
I read the un-holy fuck out of them when I was a kid (first books I ever read that had swearing) although for the life of me I can't remember how they end, and yes they are God awful in just about every way imaginable.