I have mixed feelings about 10. The good: All my old programs install and work just fine. The system is stable for me.
The not so good: I have no use for Edge or Cortana. But Firefox & Chrome work just fine, so that's what I use for browsers. And you can turn Cortana off and get a decent search capability.
There's a WiFi setting deep in the Power applet of the Control Panel to reduce power to your WiFi adapter. When this option is on, you get fine WiFi when in the same room with a router, but very flaky connections when in a different room. Easy to fix once you know about it, but it'll drive you crazy 'till you find it and change it.
They've changed the user interface enough to create a bit of a learning curve for some of the not-so-technical folks.
If you're upgrading from 7 or 8.1 you may run into driver problems, most commonly with touchpads and WiFi adapters, so be sure to check with your manufacturer to get what you need beforehand.
The "snoopware". This brings on many emotional arguments because some strongly believe it's all needed for MS to fix bugs and improve Windows. To me that may be part of it, but I have no need to have 15 of their "apps" running in the background, I don't know why they need to monitor my camera & microphone, my contacts, etc. etc. Even if their intent is 100% innocent, what if some not so honorable employee sneaks a copy of the database to criminals or maybe the government decides they want access to it?
Sooo, I don't recommend that anybody upgrade to it. But if you buy a new PC with 10 pre-installed, and you turn off the snoopware (via Settings -> Privacy), it's not a bad system. YMMV.