Hmm... i'd feel more comfortable if nokia hadn't had the track record they've had with software...but...for what its worth:

the must-have improvements:
1. HD support (scaling, recording, hdmi-out)
2. Multitouch (nice for photos and games, the rest is meh)
3. Processing Power (newer cpu+gpu)

the cool extras:
Carl-Zeiss 8MP or better camera
32GB internal + Card slot
USB OTG by default (otherwise we have h-e-n anyway...)

And as any sensible user on this forum would agree: The HW keyboard stays. Or i dont. Period.