I love:

* The fact it has a keyboard (n810)
* The whole computer in my the pocket thing (i.e. I can run port and run 'proper' apps on it with little difficulty)
* Nice clear high DPI screen
* Small size (though I would happily have a slightly larger machine if it had a larger screen - 4.8" for example rather than the current 4.3")
* The fact it's largely opensource
* The fact that Nokia do in fact listen and improve