Funny, maybe I'm a stereotypical HN user here, but I liked Metro UI. I liked it more than Material design nonsense and skeuomorphic Apple crap. Windows Phones' UI was simple, to the point, and evoked the feelings of being half-way to Star Trek interfaces. Maybe it resonated with me because of that.

Apps were part of what killed Windows Phone, but I also think they released their OS with too little built-in features. My brother used to own a phone with early Windows version; it lacked a lot of small conveniences and tweakables that were available on contemporary Android phones. I vaguely recall sharing media with other devices was a problem; not unlike how it's with iPhones.