Whoa, there was an 'easy' method of beating the final boss. It took me frickin' ages to do on crushing. My girlfriend kept telling me to leave it, as she could tell my head was close to exploding.
Yes pal, basicaly you get close to him and melee attack. You can't hit him, and he'll pick you up, headbutt you and leave you on the ground. Here's the good bit - get him close to a patch of the blue stuff, shoot it and injure him. Melee him over and over until the blue stuff regenerates. Rinse and repeat
Sh*tting hell, I never even tried to melee the bastard.