I think my main issue was the difficulty, but not the way most people seem to be complaining. I think the enemies and levels are set up really well.... except for one problem. There is WAY too much time between waves of enemies.
Also, WHY did you remove the pause from survival? EVERY game, no matter what mode, should have a pause, because you never know for sure if something is going to happen that requires your full attention. (such as having to let your dog out. It may not take long, but it does take long enough to get you killed in whatever game you're playing)