They removed desktop icons which I don't use but lots of people do. The removed the minimize and maximize buttons meaning you either have to close apps or move them to another desktop. The most annoying one for me is that they removed the system tray which just straight up broke a bunch of apps (mostly sync clients like Dropbox).
Now, all of those features can be added back with extensions (which may break in a future release) but I don't thing most people want to deal with that.
Thankfully there are distros like Ubuntu and Manjaro that patch GNOME and add back in missing features.