I had a Windows Phone.
As an OS it was not bad, especially if you tied it to a wider Windows ecosystem and you didn't mind a Microsoft version of the Apple walled garden approach.
The problem was with apps of course. The Facebooks et al were there, if grudgingly updated at a quarter of the frequency of the iOS\Android equivalents. The killer for me was the lack of 'second tier' apps - your local transport company or energy provider, or college. They all have iOS\Android apps, why would they bother their holes getting stuff rewritten a third time for a platform with a tiny market share?