Windows Phones.... at first, a refreshing new UI; elegant, minimalist, and very functional. Large credit to the Nokia design, eng, and R&D team for making such a sturdy, reliable phone in the modern market.
Sadly, it (the os) was burdened with a litany of enormous oversights in compatibility, functionality, outright inexcusable software failure (factory, not 3rd party), and a piss poor app store (a real nail in the coffin).
I've never been traumatized by a UI experience until using their phones. And I understood that going with the underdog would come with a price, but not the price of my sanity. Perhaps the Win environment is for some, but for professionals who work in the media/ent industry, they will want to avoid it like the plague. A nightmare I hope to never relive again and will warn people against for as long as I live.