Can’t comment directly on the Lumia 800. I have a Lumia 700. But I think a lot of what I say carries for the 800.
The build quality of the phone is very very good.
Gorilla glass and an excellent screen (on the 800 = LED?)
The CPU speed was a cut above any other phone at the price.
The OS is very slick. And very well designed. In particular, it’s intuitive. And not laggy.
The camera quality is excellent.
The App store is good. And the quality of some of the games is amazing.
OS is very stable.
The free Sat nav although not as comprehensive as the older symbian version – is still very good.
Battery life is very good. A whole day on a single charge with a significant amount of fiddling.
The Nokia Music app is excellent. Free music downloadable to your phone.
My gripes –
The OS is not true multi-tasking.
I’m still awaiting for the ability to use my phone as a wifi hotspot.
I’ve heard the OS will not be upgradeable to the next version of the OS – at least on my phone. Check for yours.