The advantages are technical rather than UI related.
IE11 supporting h264 codecs and DRM html5. So much better youtube/netflix support.
Enhanced network stack (although seems to be in a half finished state on win 8.x, documented tweaking doesnt work)
Better SSD support.
DX12 and 11.2
The mistakes microsoft made were concentrating on the UI changes as a supposed selling point and enforcing those changes onto PC users. On a PC, charms, metro etc. for usability is a regression. They optimised for touch not mouse usage. Dev's for all sorts of software repeatedly make the mistake that software can be optimised for touch without affecting desktop, this is complete nonsense.
I actually think the metro screen makes a good lock type screen, its good for showing live tiles, but its no app launcher for a desktop user, the start menu is best for that. Even on 8.1, search is messed up as its some kind of horrific massive sidebar instead of part of start menu.
Another regression aside from the horrific charms is that AERO no longer has glass and specifically windows vista/7 themes wont work on windows 8. Sadly this has not been fixed in windows 10. In addition the enhanced customisation e.g. the ability to shrink down fat window borders is removed in windows 8+.
So for me windows 8+ is improved under the hood but regressed in the UI. I will be migrating to 8.1 and I guess eventually to 10 but I havent had time yet to properly test it, make a custom iso etc. yet.
By the half baked TCP backend upgrade I mean that netsh is now considered obselete by microsoft yet it still partially functions in windows 8 eventho its obseleted, and there is new powershell commands to replace it, the problem is the custom templates are broken meaning people cannot do customisations, senior microsoft staff who have posted on the web have been silent when questioned about it.
Some info here.http://www.speedguide.net/articles/windows-8-2012-server-tcpip-tweaks-5077
Windows 10 is out of the box better than Win8 for sure, no doubt about it, however the fact they have now added a start menu means if the start menu apps for win8 no longer work, then win8 may be considered superior, as the start menu in win10 is not win7 style.