I installed 10 a week ago. I am concerned with the privacy problems and with what microsoft will thrust on us later. They are going to make money off this turkey. We just haven't seen all of the how yet. It looks like they plan to sell access to our personal information, charge us every time we sneeze with anything useful beyond the operating system, and shove an endless stream of adds in our face. It looks like the bait and switch model that has been used in the technology sector for decades.
I decided to go ahead and see what the beast is like, even with the concerns. Support for 7 and 8 will go away at some point. It is supposed to be years, but there is no guarantee it will not be moved up. I'd rather not wait until the last minute to figure out what I will do. I have shut down all of the adds system wide and disabled most of the known phone home features, all without hurting performance. If I can wrest control of my computer away from microsoft, I may stay with W10. If not, then there is Linux. Linux has gotten much friendlier over the years.
I had no glitches with the upgrade, even leaving all my programs and data in place. That is far superior to earlier efforts by microsoft, where a clean install was the only way to get a stable system. It did take forever to do the install. It wasn't as long as going from W3.1 to W95, but it reminded me of the waiting. I told the install not to activate wifi during install in order to keep it from sharing my passwords willy-nilly. It took a few moments to set up my network after install, but was painless once the right screen was found. I had no problems with networked printers or file sharing. It is not noticeably faster than 8.1. The new edge browser is not better than Firefox, as I'd hoped. The start menu is an abomination. Unless I haven't found the right settings, it is not as good as 2000 or Xp. It is also worse than 8.1. Either have an easy to navigate hierarchy like 2000 or a tile system like 8.1.
The only serious problem I had was that my monitor developed a bluish tint to everything right after the upgrade. It took 2 days to figure out that the monitor itself had decided to get sick at just that moment. W10 works fine with a different monitor.