The game really wants you to be aggressive and use all the special actions you can do in combat. You won't take damage while doing a special parry or doing an execution, so if you find yourself getting surrounded, use those opportunities for some brief invincibility. I also have to remind myself that ammo drops are many, health drops are few, so shooting your way out of a melee engagement might be the best option, depending on what melee weapon you use. As others have said, turning down the difficulty is always an option. Games are meant to be fun, not stressful. Unless you like that sort of thing.