Sounds like you're either not very good at this game or you're trying to complete quite difficult missions on a low stat level and/or weak weapons. I can take out a Super Mutant Brute with a few shots from the Gauss Rifle (OA DLC)
I quite like this game. Loads to do as you'd expect. Can be a bit of a chore but that goes for all RPG's not just Fallout 3








