Later in the game you'll reach a mysterious Island. The island is filled
with freaks that will make you wish you were fighting villagers. First,
there are some common enemies that have no armor whatsoever. Shoot 'em
in the head or heart. There are some that have helmets, shot 'em in the
heart. Then some big commando guy with a huge gun will start shooting at
you. Don't get hit. Get cover and throw grenades at him.
Another way to beat him easy is to make him climb windows. Shoot him
while he's climbing a window.

Eventually, you'll reach some fortress and you will find some big guys
that look like cyborgs. Its best to shoot at their heads with the rifle
or magnum. As if things weren't bad enough, a new creature called "The
Regenerators" will attack you. If you shoot at them, their body parts
will grow back. The best course of action is to run past them and do
avoid getting hit by them. Eventually you'll reach a regenerator with a
keycard stuck to his torso. You have to kill him, shoot his legs, when
he falls to the floor, throw grenades.

Buy the body armor from the merchant. It reduces all damage taken by
30%. Dont waste ammo and you wont have much trouble. At least till you
rescue ashley, then it gets extremely hard.