The Nexus 5 has the opportunity to pull a lot of disenchanted iPhone users to Android. What would it take for you to make the switch?
I'd also like stronger per-app privacy controls and sandboxing. I have this vague idea that installing the wrong package on an Android phone can mean doom, and that many apps request permissions that are far too broad and on install time (rather than when they need them). I'm unsure whether I'm just ill-informed on this or not.
That said, I'm not a disenchanted iPhone user so perhaps your question wasn't aimed at me. I recently upgraded to a 5s and am very happy.