I am of course talking about the amazing fan fiction written by Nick P (not me). Also known as Spineless-Mush over at PortalForums.net. This book is simply called DOOM and is, as you guessed, based off the Doom universe. Through the upcoming years that eventually lead to the release of Doom 3, I read a bunch of fan fictions based off Doom. And while the Doom universe itself lacks any real story or dept, it does contain some of the coolest monsters and environments I've ever seen in a game (or movie for that matter). But most authors of these fan fictions couldn't put these aspects into a dark, demented, engrossing, and most off awesome story that Nick P. wrote.