N90

The N90 is the only Nokia N-series I had seen before, and has entirely too many hinges to be something I'd consider usable with a single hand.

New hi-res screen and improved screen fonts.
Fast. Like no other Series 60 before it (although based on previous experience all "blank" Series 60 phones seem fast before you start filling the memory with contacts, photos, etc.).
Decent quality pictures (although the Carl Zeiss lens doesn't look like much of an improvement on the K750i).
High framerate video.
Same camera UI as the N70.

Big, Heavy, Fiddly. Feels like a Transformer's pet rock. Doesn't carry comfortably in trouser pocket (unless you're an XXL sort of guy/gal).
As usual, not enough RAM to last more than a couple of hours in my hands. A couple of shots, a few contacts, and poof.
Incompatible with some old applications I had lying around (might be this revision, but it's common enough between different Nokia models).
Lens gets dirty easily.
Camera stick and button are fiddly.
Memory slot cover seems... likely to snap off, like in the N70.
New charger plug (oh yes, they're changing the power adapters, and it ships with... an adapter for the adapter)
No infrared.