The OS was absolutely rock solid
Battery life was amazing Office 365 worked great
The camera hardware was excellent
The Bad:
The handsets did not look sophisticated.
The UI was utter dog shit. Joe Belfiore should have been forcibly marched out the door for pushing that abomination.
The complete lack of variety of third party apps
When they were available they were almost always severely limited compared to the iPhone and Android versions.
The key internal apps like the Camera app were limited.
They didn’t come up with a free development solution that would entice Android devs to target both.
To sum it up they followed a mad man with mad ideas and then doubled down on the bad idea out of pride.
When they finally wised up they didn’t do even 10% of what was needed to recover.