It's quite good but I must say I'm a little bit disappointed. Some points I should make -

Personalization - I think for some people the icons in the taskbar may seem too small so there should an option to enlarge them.Also, the customization options could be more elaborated.

Resource - Cortana is using about 100 MB of RAM when it's up and running.

Settings - Might seem complicated when it comes to make some changes in Windows Update and others.

Onedrive - Pain In The *** (For Me)

Boot Up - Before the upgrade, I heard everywhere that Win 10 has faster boot speed. But I don't see any difference between this and Win 8.1 and to be honest I think it's actually slower.

And a weird thing I noticed, when I first installed Win 8.1, an unknown device appeared on my device list but I could install its driver by using Windows Update. But I can't do that in Win 10 with the same device. It just couldn't find the driver.