Some of the problems that are experienced by some people, with upgrading an operating system, are incompatibility issues and things that end up corrupted in the course of upgrading the OS.
I've experienced this in the past and that is why, this time, I chose to NOT have any of my computers upgrade the OS.
I have nothing against Win10, per se, because I've not used it yet. But I am familiar with things that CAN happen in the course of upgrading an OS on an existing computer, so I stay shy of that now.
I'm going to keep my computers with Win7 and Win8.1 and, should the time come before these are no longer supported by MS, I'll purchase a Win10 (or whatever the OS du jour is) computer with no problem.
But I really AM glad that many people have upgraded and not had problems with their computers. Computer problems are so far beyond frustrating that I don't even want to think about it, as I'll get anxiety! 
I'm in the middle of changing my ISP (tech coming over today) and I'm just anxious that it won't go well, especially since I've already changed my email addresses at a ton of sites. Will be glad when that's over! You never know when something might go smoothly, or it goes kerflooey!