I have both.
So far I've played DOOM twice and I'm barely past the starting area of Fallout 4. But I'm in a "fast paced, badass, metal" FPS mood as of late. I can only do so much "exploring" and I'm also playing Dragon Age right now, so that takes up my "exploring" budget.
Fallout, like the games before it, is a "Fight a little, explore a lot" game. Doom is just the opposite. "Fight a lot, explore a little."