Right now I'm on what i assume to be the last level in the game and on extreme difficulty, its ridiculous, i have spent the last 10 minutes trying to find out how to get past a dude with a machine gun that only appears when i hit a certain point, a point that leaves me wide open for a bullet. So I'm wondering is anyone else  having this problem on extreme?

Tried co-op? I think I know which part.

Yea I agree, I played through on easy and thought it was retarded how accurate the enemies were. I can only imagine on extreme. I much prefer developers throw more guys at you and make your health lower instead of just making the enemies have pinpoint accuracy so that when you stick so much as a finger out it gets shot off. At least it's not as bad as World at War and getting 5 grenades tossed at your feet every time you step out.