Exemples how NOT to do it: Dwarves in Stalker. They midget bastards will rip your guns from your hands and send them flying, will drain your entire stamina, making you immobile, they have a protective shield imprevious to damage they can put up at any time, AND they have noth ranged and melee attack.
You'd think they would have barely enough hp to survive a single magazine from a simple assault rifle, but no. Those midgets will take a beating, and only an ultra rare rocket launcher round, or well placed sniper rifle rounds to the head will end the battle quickly, without spending either a fortune in medikits, healing yourself to knife them to death, or even more energy drinks to keep stamina at the max level to shoot them without losing your weapon.
I hate those fucking dwarves.