A lost opportunity
I've said a few times and I'll say it again - Windows Phone is / was a good platform. The bad thing is how Microsoft treated it. Instead of regular updates adding features that people wanted they treated it like Windows with big updates once a year at best. Early in Android's life they iterated quickly with features coming thick and fast and I really feel if they'd done similar that it would have had wider adoption.
The UI took a little getting used to but it was clean, quick and suffered none of the normal slowdown or jittery scrolling I'd associate with iOS and Android at the time. It's almost criminal how badly they failed with this but that's Microsoft for you. It probably didn't help that they effectively released an OS that was a dead-end with no upgrade path for phone owners in WinPho 7. Any early adopters were basically screwed in a massive way for giving it a chance. Yes, their phones still worked but most new features were only available to WinPho 8 devices.
I will miss the potential it brought with a fresh take on things. I will not miss how badly Microsoft handled it and failed users, developers and the OS by treating it like Windows in almost every way.