First, if there's already another thread about this, please move this. I've had denim 8.1 on my 1520 till yesterday. I haven't had any interest in upgrading my phone because of all the negativity I've seen on here about 10 but my Xbox music app quit working in the beginning of December & I haven't found an app that I liked to play my music or that would sync with Bluetooth so I decided to take the plunge just so could use default music app again. The upgrade took bout an hr & half, I did a soft reset right off the bat, woulda done a hard reset but honestly couldnt find the hard reset at that point Im sure there is problems that people have with windows 10, but in the 24 hrs I've had on my phone, I haven't had any issues & love it!! My phone is like a brand new phone & the issues people seem to have with Edge, I dont seem to have. Takes less than a second to switch between pages. There are little things that are kinda annoying but that's only because their different than denim but definitely not deal breakers. My phone is 2 years old & on second battery but so far runs better on 10 than did on 8.1. I was having random reboots on 8.1, I dont have that now. So anybody that is scared to try 10, I just want to say, form your own opinion, try it and see for yourself how great windows 10 really is! ☺