Gnome Shell anybody? I'm surprised nobody brought it up yet.
About 10 years ago I switched from Gnome 2 to 3. Because my distro did. It was a huge drop in features. Over the years I had tuned my desktop experience on Gnome 2 with different panel apps, layouts, some custom hacks. It worked great. Gnome 3 ended all this. It was really simple, so that it was almost dysfunctional. It was new so I thought the community would soon catch up. But it never did. The experience is still much worse that in the Gnome 2 days. Even a few extensions that try to mimic the Gnome 2 experience can't really compensate, and many of them break with every other update. It's such a shame.