I got lucky and made it through the mortar section on my 3rd go overall and my first attempt at the mortars. I had more trouble with the very last checkpoint trying to use that gun to take out the tank.
For me the hardest part of the game was probably the furnace room as there was really no cover that left you safe. I eventually just threw a few smokes and made a run for it down the right hand side after nearly 3 hours of watching Keith auditioning for a role in the TV version of the A-Team. He would unload a full round at an enemy from 10 feet and hit nothing but air. In the 3 hours I tried to get through that god forsaken room all he managed to kill was me 3 times with wayward grenades.
The other sticking points I ran into where most of Laison River as I had next to no ammo, the Germans guarding the Flak's kill you as soon as you pop your head out, even through smoke and one of them is invincible except for a rifle butt to the face. I had to use all my smokes here as once you've planted the C4 you can't run away as they ALWAYS get you before you get to cover so I had to plant the C4, throw smoke, wait then leg it. Also not giving you the checkpoint until you have actually pushed past the last Flak was pure evil as the Germans kept respawing on the hill. Then of course I got to the house with no smokes left and died quite a few times trying to reach the front door. The run from the checkpoint to the house was really getting on my nerves.
Trying to get up the hill on "The Island" was a frustrating experience as well even with smokes. What made it worse was that once I got to the top (taking the right hand side route) my team regrouped at the top but didn't kill a couple of Germans away over on the left. Instead they all just sat around looking at each other while those 2 took pot shots at me, and me only. Even the guys running up the left hand side got ignored, they focused entirely on me. As soon as I popped my head out of the bunker the bullets would fly. I had to throw a smoke for cover then a couple of frags to get rid of them, unbelievable.
I didn't even get to see my Grizzled Veteran pop up as I only made 1 run through so I ended up with the "2 for 230G" pop up instead.