I feel like you should embrace taking damage. One thing I really loved in the new DOOM is that managing your health is part of the combat. It disincentivised going behind cover. I think having some health management, would be really great with this game, and would also allow you to put in instant damage enemies without the player feeling like it's unfair. If you still don't feel like that's enough though, you can do like Bioshock did and make the first shot from enemies always miss.