I like Windows 10. It works just fine on my computers and I have had no issues with it. For that matter Windows 8.1.1 worked fine too. It's all about the shortcuts. Learn them, use them, love them. They make navigating the OS so much easier. You would be surprised how many people I need to tell to right click the start button to get access to all the power user goodies. And it's customizable too with some poking around. That is one feature that I sorely miss anytime I have to go back to Windows 7. Makes Windows 7, which I loved, feel...clunky by comparison.
As for the privacy concerns. Hogwash. Google does worse, and I have yet to hear of one story of someone getting stalked, sued, or otherwise thrown in jail for legitimate, legal use of Google Now/Cortana/Siri. In fact I am pretty sure Cortana, unlike Google, doesn't sell any metrics to third parties. personally identifiable or otherwise. I believe there was a podcast on another windows website that answered that question. You can't have your cake and eat it too. If you want to know when your next appointment is, notify you of phone calls/text messages/emails, and have all of that done through voice activation as has been not only promised, but ACTIVELY REQUESTED for the better part of two decades, then you gotta give something. So either set back computer usage two decades, or take off the tin foil hat. Can't do both.