I didn't like how locked down the Windows Phone OS was, even for the time, and I didn't like some of the limitations that popped up around app capabilities. But

I didn't like how locked down the Windows Phone OS was, even for the time, and I didn't like some of the limitations that popped up around app capabilities. But otherwise, agreed, they had some good UX ideas, I liked their interface a lot, there are concepts there that would still hold up really well today on a mobile OS. And it was certainly (imo) a lot nicer to develop on than Android. But... yeah, the app ecosystem.