Well, I had my first real experience with Windows 10 yesterday. I'm a computer geek, power user, web/server/db administrator, tinkerer, etc. We got a new laptop in the office for testing.
For me, Windows 10 is a dramatic step backwards in usability and UI efficiency, compared to Windows 7. There's way too much bloat, it's a nightmare trying to find all the settings you want, the bundled apps are intrusive, and you have a lot less control over the UI (and everything else). For a person who wants their computer to act more like their phone or tablet, it might be ok. But from me, it gets a big thumbs-down. I'm ambivalent about the visual aesthetic, but the new Start Menu is atrocious, and there's no option (short of installing Classic Shell) to use the old-style.
Alright, that's enough ranting for now. :)