I'm playing through it on Crushing too, there are a few battles I'm really not looking forward too given how tedious they were on hard, and how many enemies you had to kill between checkpoints, specifically (that I can remember):

(SPOILER)
1.A bit before you get onto the cruise ship, in the huge area where there are the two mounted guns and you have to swim around a bit. So many enemies there.
2. On the cruise ship in the main concert hall or whatever it is. This one sucks if you fail the first time around because you spawn in a stupid place.
3. Right at the start of sink or swim, when the area you're in is flooding.
4. When you hit the convoy.
5. When you're in the desert and you have to take out the trucks with RPGs

I imagine ragequitting at one of these stages and not going back for a few months.