Not too great so far! I still prefer the more 'desktop feeling' Windows 7! I have a Dell Inspiron 15R (core i5, regular 7200rpm HDD) and on this laptop, my Windows 7 loaded way more faster. The startup of Windows 10 is very similar to Windows 8/8.1 in terms of slowness. It all feels like Windows phone loaded onto my laptop and I totally dislike that feel of a Windows mobile OS.
Cortana occasionally crashes, when clicking on it to activate Voice search. The only feature I've liked so far is the multiple desktops. Let me see if it grows on me. I have been more disappointed than WOW'd so far.
Cortana is horrible. It doesn't even get my accent. Heck, even Siri gets my accent right. Having lived in the US for 14 years now, I have a good enough accent to get recognized by most voice recognition systems. And most of what it gets right, it takes me into the Edge browser (as if to say "I'm promoting Edge for god's sake).
The taskbar tray and the minimize/maximize/close UI is pretty mediocre to poor. Who the F worked on the UI for Windows 10? This one feels like one of the dev builds.