Microsoft's latest revisions of the WinPhone were software engineering wise the best mobile phone OS on the planet. As you say, it was quick, silky smooth and yet ran on low end hardware with excellent battery life. I gather they achieved that buy tightly locking down how software developers could do things. Perhaps is why their app store was so thin which was major factor in their downfall, but still it was a remarkable effort. I take my hat off to that team.

It as even more remarkable because if you went back a few short years WinPhone was the worst phone OS on the planet. It crashed regularly, a misbehaving app could drain it's batter in no time, and the UI was horrible.

So much for "if you build a better mouse trap them will come" I guess, especially if your reputation is for making crap mousetraps.