I used a windows phone for a while and while the ui was good, it failed in some critical ways and because the people at MS had their heads to far up their bosses asses, there was never a fix.

4 things that were game breakers (iirc, it's been a few years):

1. if you set the same alarm every day, then the alarm worked reliably. If you set a special recurring alarm for 1 day in the week (at the time I had to get up early every Friday), then that alarm would work once and then not anymore after that.

2. if someone send you an sms (or a number inside an sms), then it was not possible to add that number to contacts. You had to manually open contacts and type in the number.

3. the app store was forced localized and if you lived in a small market, you could only see reviews and review scores from that market. Not all apps where available either. With how few users windows phone had, there were no useful aggregated review scores available, only dodgy ones. Fortunately there was a user made app with which the global store could be opened, but as an out of the box experience, it sucked.

4. the app store was filled to the brim with the lowest quality shovelware in existence. I once went in to find if Firefox had an app and I found a shitload of apps called stuff like "install Firefox now", each for a small amount of money. So I went to Google and found that there was no Firefox app yet and those were all scam apps. If the Microsoft CEO then goes on the news and proudly proclaims how many apps their appstore has, then you also now that they had no intention of ever fixing this shit and it was going to stay shit forever.