I have used it – I had a (piece of crap) HP ENVY 15 I’ve just sent back for refund and I went from Win 8.1 to 10. I’d say W10 has a slightly updated 8.1 kernel (pretty fast) and a new graphical interface which isn’t horrific but has a few foibles of its own:
The start button doesn’t give you an hierarchical list of programs but an ‘a to z’ listing which can be a little confusing.
New tech in W10 (not MS’s fault really) is display scaling. As a result if you have a 1080p display or higher some programs (including MS’s own, such as device manager) will appear fuzzy as they don’t understand it, or appear much smaller as they are pixel based.
I’d say a mixed bag. If you could get W7 interface on a W10 kernel then that would be nice. Classic shell still works, so I hear.
Overall – better than W8 but not as usable as W7. I can’t comment on reliability as my ENVY 15 was a bag of poo and kept crashing, regardless of OS. 🙂