What Tweak, Program, ... changes a Desktop Environment from unusable to great for you?
I have used Linux on and off for 15 years. I consider myself a casual user and stuck to the mainstream DEs (mostly KDE, XFCE and some Cinnamon).
Gnome has been a hurdle for me before and after the big version 40 changes, I couldn't get my head around how they handled the workspaces and workflow. At some point I I tried out an extension hat changed all of it.
It moves the workspaces to a vertical panel and the programs onto a horizontal panel. In a workspace you can view the programs full screen or tile them.
Several Programs inside a Workspace.
It's basically they same way Gnome works. However for some reason it just makes sense in my brain. No idea why.
(I'm looking at WMs that work in a similar way atm. Maybe I'll take the plunge away from DEs at some point)
Has such a small change ever saved a Desktop Environment for you and is essential if you ever install it?
I really like compositor/wm/DE which allow for keyboard driven movement of windows between workspaces and workspaces between monitors. Especially the latter requirement is only met by a few wms, e.g. sway/i3, hyprland.
I can't stand it if switching to the next workspace all workspaces on all monitors change. This makes it annoying to use with a second monitor that mostly display the same windows (e.g. messaging, video, docs).
That's true, most WMs have a simplistic workspace geometry, where they spread a workspace across all monitors (regardless of their placement). I suspect that, since the workspace abstraction comes above monitors it may not even be possible for them to have a workspace split between monitors.