For me this was the starting point.
After or around the same time someone from Gnome (or Red Hat?) realized (at least this is how I remember their marketing) humans think spatially - and used that observation to decide that everytime I click on a folder in Nautilus it should open in a new window. (Yes, it becomes a mess really quick.)
Also the insistence on removing every configuration option.
Same goes for Unity: my best explanation is someone heard Mac OS had great UX and decided to copy it wholesale: Move controls to the left. Change Alt-tab. Introduce dock.
Common for all these "improvements" is that nobody asked us users, and nobody cared to make it easy to go back.
I now have an acquired distrust of ux designers (and I am really happy whenever I meet good ones which thankfully happens often where I work.)
- Ribbon has mostly been fixed now, and is mostly pleasant to use even if the File menu is still jarring.
- Nautilus was fixed in the next major version.
- Unity was never fixed. I hear some people like it but I guess we are a good bunch of old Ubuntu users who cannot stand it. More importantly it is hard for me to see any reason besides arrogance for why there couldn't an option somewhere to get back to normal alt-tab.