What makes Linux appealing to me is the extent of customizability, but I didn’t find many answers when looking up with desktop environment is them most customizable. Some say KDE is most customizable than say, Gnome, but doesn’t Gnome support CSS customization while KDE doesn’t?
The average user isn’t going to be going into the guts and changing code. For them customization means the number of exposed “knobs and dials” they can tweak. In that regard KDE is far more customizable than Gnome. I’ve not played with others enough to evaluate them fairly.
To modify most settings in Gnome, if I remember correctly, you needed an addon. Granted, last time I ran Gnome daily, they were still on Gnome 2 and Ubuntu hadn’t come out with Unity yet.