I really enjoy the D4. My biggest complaint is battery life, but idle battery life is very good. I can easily get ~ 2 days off the battery if I don't touch the phone (which is good compared to the D1). Once you start using the phone, battery life goes way down.
Heavy use (using location aware apps that are not navigation, and lots of 4G data) I get around 8hrs (!)
Normal (for me) use I get around 22hrs.
Right now my battery is at 82%, 5 hours 11 minutes off the charger and 15 minutes of screen on time.