It better be a) cheap, b) comfortable and c) universally phone-powered. Seriously, I don't want to spend $500 on a VR headset, the GearVR is at least a step in the right direction
Eye-tracking and better FOV.
I don't know if it's sensible to expect these for the second gen, but I certainly do want them before I even consider jumping into VR fully.
Smaller headset, wider field of view, wireless (may take another couple generations), better graphics (comes with the generational leap) and eye tracking.