I upgraded my work laptop and my wife's convertible laptop to 10 today.
Some stuff I like:
If you have a non-touchscreen machine it works more like 7 with a Start menu (plus unobtrusive mini-Metro interface). If you have a tablet it works more like 8 with the touch-friendly Metro interface. If you have a convertible laptop you can have it work one way in laptop mode, and the other in tablet mode. You can also configure it to always do one way or the other. In other words the way 8 should have worked from the get-go.
Multiple desktops. This is huge for me for work. Also a decade+ behind the ability to do this in Linux; not sure why it took them this long to implement it in Windows.
Microsoft Edge actually seems like a really good browser so far, though I'll reserve final judgment until extension support is added this fall. I do think it was a branding mistake to make the "e" icon/logo for Edge nearly (if not completely) identical to the one for Internet Explorer. People don't associate that icon with good things . . .
In-place upgrade process went flawlessly. All my hardware and programs seem happy.
About the only thing I've run across so far I don't like isn't any different than one of my annoyances with 8.x, namely the pressure to link everything to your Microsoft account. Cortana (the Siri equivalent) will not function if you don't link the account, and some other apps as well.
It's only been a day, I'm sure there will be more things I don't like, but so far so good.