It all depends on personal taste, you like a windows interface and a windows feel to your gadgets, then you would love WM, everything has pros and cons to them.
I started with nokia, and from there on I hated symbian 60, it was buggy and slow as hell, completely ruined the os for me, moved on to ericsson and worked with symbian uiq, which was a revelation and buried nokia for me completely.
From there I moved to an imate and wm5, did not have real problems with the os, but I think the phone itself soured wm for me, went back to ericsson and uiq, and now I am on iphone (osx), currently I love the iphone's os, especially the ease in which you can delve into the os itself
But again, its all up to personal opinion