I've been using Windows 10 for a while now. My upgrade had its issues. I was having an issue at first with Cortana not working, but every time I tried googling it, I kept coming across posts describing a different problem where the start menu wasn't working either (my start menu worked, it was just slow), and of course, the solution didn't fix my problem. I eventually had to uninstall and reinstall the upgrade, but it's worked ever since. I should also probably mention that upgrading from Windows 7, which I did on my dad's computer, wipes out the pre-installed games, but there are websites where they can be downloaded.
Other than the upgrade issues, I like it. Better than Windows 8/8.1, which I had before. I mostly just like having the start menu back and not have to deal with the tablet OS running on a laptop that was Windows 8.