+1 more RAM
+1 not that thick as N900/N8
+1 car navigation (which would probably not crash every few minutes as Sygic solution does on my N900)

Off topic:
-10 no replaceable battery (makes the device unreliable)
-1 different SIM card size (unable easily to swap SIM cards to other phone as N9 dies, again does not allow to recover from unreliability)
-1 no hw keyboard
-1 no cover for the camera lens
-1 no SD card support (for memory hungry apps as offline wikipedia, additional offline maps,...)

Off off topic: I want one, even if it is expensive, stupid and unreasonable idea.