[zanny]

Gnome is practically only usable through extensions. If you want an example of Gnome 3 done right, look at Zorin - which is a Gnome reskin designed to emulate modern Windows.

Likewise, KDE is highly modular and configurable - you can develop whatever widgets you want and drop them in wherever you want. That is how they now have a mobile and desktop variant of Plasma. And the configuration means you can do everything from featureless software rendered uncomposited desktop to exploding windows and spinning cubes in OpenGL.

The thing is highly extensible means more space use, and LXDE / XFCE in part originate in a desire for smaller footprint installs. They also use less memory on average, albeit the usage of Gnome / KDE and them is minute relative to modern memory footprints (XFCE might use 100MB, KDE sans semantic desktop search might use 200).