Windows 8 was when Microsoft tried to cater more towards Windows-on-tablet use cases. Which lead to everyone, including desktop users, having a fullscreen phone-style app menu take the place of the old start menu. This, for desktop use, is obviously quite disruptive and was hated by everyone.
They addressed most issues in the 8.1 update, like a year later I think.
You know what was worse than desktop users? Server users via RDP.
There was no start button. There are no screen edges to swipe in from. Hot corners are really hard to hit. I still can't believe somebody said "yes, good idea" to using that UI for Server 2012.
I RDP'd into a Windows Server VM a year or so ago and got a full-screen popup for Edge or some shit like that.
If that wasn't bad enough, the popup was a web view, meaning none of RDP's acceleration/client-side compositing was in play and I was greeted with a ~1fps slideshow.