I'll start. I definitely miss a handful of things but one MW3 quality of life survival feature that was removed was the ability to skip the round timer.
I ran the numbers and if you want to go to wave 55 you're guaranteed to spend atleast 22.5 minutes just waiting for the waves to start. That's insane
Some other quickfires are:
Can't use buy stations mid-match
Can't crouch dodge helicopter spray
Juggernauts seem to be immune to tacticals
No buyable friendly ai squads
And so on..
But that's just my handful of nitpicks. What do the rest of my fellow survival players think?