My single personal experience of a Windows Phone came a few years ago when my 70 year old dad was sweet-talked (i.e. conned) into 'upgrading' to one by a salesperson in an Orange shop in Birmingham. He tried his best to use it for a week or so, but could barely work out how to make a phone call, much less input contacts or anything else.
Now, I know many of those reading this will scoff that "he must be some kind of technically incompetent luddite", well yes that may be, but he's a just a normal human being, and he's used Windows for many years seemingly happily. We may be all geeks here, but we're not the norm; what comes easily to us, doesn't to most people. And that, for me personally, was Windows Phone's major failing - the interface was just too alien for your average person.
Fortunately the story has a happy ending, I bought him a cheapish Android phone, which he figured out how to use almost immediately.