I'm pretty wary of Windows 10 Mobile (is that the right nomenclature?) but Windows Phone 8.1 is fantastic and I think probably the best user experience available on mobile. It is certainly at least comparable to iOS and Android. I most recently came from Android, switching from a Galaxy S3 to a Nokia Icon, and the Windows Phone is much more of a pleasure to use, in my experience.
My only real substantive complaint is that there aren't enough official apps (e.g. no Snapchat) and the ones that do exist are often obviously the ignored stepchild for the developer. I can see how the ideal of Continuum would be nice, but on the other hand, I suspect they're going to mess up a good thing.
If you haven't used Windows on mobile since the garbage that was Windows Mobile, or the halfway-there Windows Phone 7, then it's worth looking at again. But that's also part of Microsoft's problems: they fumbled so often on mobile and people haven't forgotten.