dude this guy just wont die for me. i take out the four green things on each side of him, then his four eyes, but after that i cant seem to take any more damage off him. Ive tried the chainsaw with no luck. this is pissin me off

I wish i could help but I am at the exact same spot you are, can someone let us know?

I figured it out last night, here is what to do:

Shoot all of the sacs/circle weak areas on the green eyes sides

after you have shot them all more of them will show up on his head, shoot them as well

after you shoot those it will turn into one big spot on his head and he will go completely apeshit and start charging like crazy, all you have to do is keep pounding away at the large spot on his head and he will die.

For all the smaller circles i used chain guns and than for the final big circle i used a chain gun rocket launcher combo.

Happy hunting