My key complaints:
(a) Battery life is not great. If you charge it twice daily, no issues. The battery dies faster if I use the internet or audio/video or Bluetooth a lot.
(b) The cable headset that came in the box (WH-701) did not work well with my phone. Some problem with the jack-socket coupling - sound was always weak and the headset controls never worked.
(c) Some applications for the N97 Mini have been highly buggy: they crash and/or don’t work as they should. I’m not sure whether this is Nokia’s fault, Symbian’s fault or the application provider’s fault. But the applications that are most important to me have all worked without any trouble: Nokia Email Messaging (to access my Gmail and Yahoo accounts), Opera Mobile, Calendar, Fring, Nokia Maps, Google Maps, Music Player, Radio...
(d) the touchscreen doesn’t understand dual contact (e.g. you cannot zoom in or out using two fingers) and is not sensitive and easy to use
The N97 Mini is the best Nokia phone I’ve owned, basically because it does so many things - more than those done by any other Nokia phone I’ve owned. It is not too heavy given how feature-rich it is. Build quality is good too.
But it’s not perfect - lots could be improved: (a) the bloody battery’s life, (b) the touchscreen’s sensitivity, (c) the OS doesn’t respond as fast as that of Blackberry or the iPhone - an old Nokia/Symbian weakness... I could go on. But both the Blackberry and iPhone have enough missing for me to still prefer the N97 Mini. Of course, Ovi Store is no match for iPhone’s app store.
Ultimately, the "good v. bad" calculation really depends on the features/capabilities/attributes that are most important to you - and the quality/condition of your individual handset. It sure seems like a lot of people ended up with bleep handsets and/or defective firmware. Best to check every feature and app out early so you can return it in case you discover any problem(s).