I beg your pardon but Modern UI (or Metro UI when its first called in 2010), is what brings me to the Windows Phone platform in the first place, despite being questioned and ridiculed by my friends and family who uses Android or iOS.
I felt iOS and Android bores me very quickly with its icon-driven interface and the overall skeuomorphic interface back in the days. Modern/Metro UI however, despite being basic, but at least it made the overall UX more alive compared to the dead icons and text in Android or iOS. Sadly, Microsoft is killing off the unique UI for the sake of gaining marketshare and users from those respective platforms.
IMO, the UI is the centre stage of a phone OS, apps aside, it gives the OS its character and charm and set itself apart from the competition. Windows Phone and WebOS are the those pioneers, unfortunately, being unique doesn't seem to translate well to usability I admit.
I hope it is not too long or you won't read it, but once I manage to get my hands on a Windows 10 for Phones build, I will make a detail review of Microsoft's Android-ish UI direction.