In order of importance:
1. MicroSD port
2. back-facing camera
3. gorilla glass - It's small and will get dropped a lot and will knock about in handbags and backpacks a lot. Corning glass is good, upgrade to gorilla is better. I'd pay $25 more for it as an option.
4. Mini USB port - increases access to storage options.
To be honest, none of these is very important. It's new and great and I don't want a new one right away!
HDMI port not even on my list. Please don't make it bigger.