In my opinion the N9 is missing
- an upgrade path (i've resigned to this)
- glove support (no stylus, will be a biting pain, starting October)
- spare battery support
- pressure levels (i used them on the N900, but not a lot)
- a symbiotic relationship with a Qt-based OS which developers believe have a future (it used to have that)
- screen estate during typing (yes, you know what I mean)

Lack of glove/stylus support means I would as a matter of fact answer fewer phone calls and use it less than the N900. It's a real difference for me, living in this climate. I'm already on a capacitive screen now, and it's a step down.

Lack of spare battery support will be a pain when I'm on national guard exercises and can't easily charge the phone.