Windows 8 and 8.1 was a right mess in the UI part to be honest, no one knew what it wanted to be, far better once the start screen was replaced with a start menu, I now find Windows 8.1 usable, mainly because most of the modern apps stay away, ok you need to make files default to different apps, like audio to media player instead of what ever MS wants us to use, but that is easy sorted, not that I use media player.
I never said that Windows 10 did not work on conventional desktops or laptops for that matter, but it is very modern app orientated and they seem to pop up when you don't want them, even getting software as default is not as easy on 10 as it is on Windows 8 or below.
Take your browser, go into your browser settings and set it to default, you will find it will not do it, instead it may pop up a Windows 10 setting dialogue box, in which you can change it or it may just pop up a notice telling you to go to choose default app settings.
Then when you do get things all nice and sorted Ms does a big update and muck it all up again so you have to start all over again.
The way Windows 10 uses Modern apps is worse than Windows 8.1, at least with 8.1 they was on a separate screen. Modern apps are for touch screen, that is why they are so clunky.
I know the Calculator works on touch screen or with a mouse and pointer, but it just don't look nice and it is only a better product if you use all the new functions.
I do not think it will take long for Apple to follow Windows, OS X is getting that way now, I expect Apple is working on a OS to work on phones and and their desktops/laptops.
MS had to do something to up their game, since their mobile phones have not really done very well, so I think Windows 10 is the last ditch attempt to get people to go for Windows based tablets and phones.
I tried a Windows phone yesterday, while I have used one for a few mins before, yesterday was the longest I have had a play with one, it was a windows 8.1 and not 10, but they still more or less work the same way, Not something I would buy to be honest, I never liked the tile system on a computer or phone and to be honest the apps that are available are not that great. I do not know if the phone can be updated to Windows 10.
My mate who owns it have to get used to it now as it is the first smart phone he have had and I thought it may have been a easier one to get used to, but I have my doubts.
Sadly I have to stick with Windows on my P.C due to my hobby, but the type of software I use is getting better on Linux.
Desktop machine now powered by windows 8 pro 64bit, no dreaded metro and Linux , laptop by Linux