First off, you have to make sure the Kryll are scattered. Definitely the torque bow helps (it took me awhile to figure this one out). Just shooting him in the head when the kryll are around won't do any damage to him. With the torque bow, shoot at him and the explosion makes the kryll scatter. Once that happens, unload on him at his head with whatever weapon you have and only using the torque bow to scatter the kryll. If you have the sniper rifle, that works wonders.
Using the bow 4 or 5 times seems to be the amount needed to defeat him.
Also, stay in the light or the kryll will eat you up. Also, he keeps moving close to you so you'll have to eventually run to the other side and I suggest getting behind a barricade to protect yourself. Just make sure it has light around it to keep those darned kryll away!