I had a Nokia Windows Phone and I still miss it. It's best feature (for me) was that it was fast. I hardly ever had to wait for it to catch up.
But that was of course running only the few apps available on the store. Any third-runner in a space is never going to get enough attention from 3rd parties to survive.
Part of that "speedy" feeling, I often describe as the UI feeling almost slippery. Like everything on the glass just slipped across your fingers. The keyboard was amazing, and so quick.
I thought moving to a 120hz display would get that feeling back, but it still doesn't have the slippery feeling.
I had a few Windows Phones too. The thing I loved was the lack of hamburger menu: UX standards put controls at the _bottom_ of the screen, or on a pane accessible via swipe. It was all within thumb range. You never had to awkwardly reach to the other end of the display or use your other hand.
But that was of course running only the few apps available on the store. Any third-runner in a space is never going to get enough attention from 3rd parties to survive.