Firstly destroy the big gun on its back because this will take the most damage out of you. Make sure you use the minigun on it because it will be alot easier. Then destroy the little guns on its sides and finally destroy the things that fire plasma grenades. By the way if you run out of ammo in your minigun use your plasma autorifle.
The very last boss is even easier!Just disable its guns first then destroy its feet, and bingo!Go round the back and blast it to bits by sticking a rocket on your K-SMG!Repeat this about 3-4 times and youve completed the game!
I really could go on all day going through a complete walkthrough as ive completed it on easy normal and hard and nearly done all the challenges and leagues. I found it easy but im not sure about you lot though.