Having a button to look behind you could be cool. It would represent looking over your shoulder. This would be possible while walking or running. It would allow you to see the horde behind you etc. 'that would be OP' i hear you cry! well to be honest when moving away from zombies the biggest threat is whats in front of you. zombies are slow and can't catch up with you in most cases. Not looking where your going would be very risky! You could run into a horde of zombies or simply fun into a wall.... so whats the point of looking back? Well to see whats going on, to see what interesting stuffs happening. Also while looking forwards it would be nice to lock the view dragged forwards, so you have maximum view distance. Also I'm sorry as I imagine these two points have been mentioned before.