I've been playing with Windows phone for a while now and I feel sorry for Nokia. From my experiences, windows phone is nothing but pain for advanced users and too complicated for normal users. Here goes few points noted so far;
User interface is complicated. No matter what, I am quite confused all the time when using phone. For example switching between applications is some how confused. Ordinary tasks like forwarding someones number to SMS is pain and I am always lost where I am with this phone. Maybe it's just me.
I don't need xbox live etc stuff on my screen, make them disappear. I need text editor to type quick notes, straight and plain. No flying tiles and partly shown title text and other candy.
Biggest problem is music, video and photo copying to and from phone. When I plug my phone to Linux, nothing happens. Making things dependent of some proprietary binary is no go road for most of users. I see big troubles in this.
And for last; SDK's. We made program for this phone and compared to other platforms, microsoft is pain. $99 money needed, no file based deployments to phones and totally unacceptable code ecosystem for todays open source users.
Nokia, you're on wrong train now.