I'm now a level 14. Been running around with this:
Stopping power perk (forget what the new name is called, and does it actually make the gun stronger or just help bullet penetration through walls?)
I've been doing alright, it took a while to become good again though. I started off with like a .8 k/d, now at 1.5 though so it's good. The levels so far are confusing though. And the campaign is fucking awesome, just beat the level that I was stuck on... so much fun.