To me KDE 1 and 2 looked great. KDE 3 and 4 were just ugly and unusable.

KDE 5 and 6 look ok I guess, but are buggier and perform worse than XFCE, so why would I ever use them?

The "Win95 pixel art" era:

https://en.wikipedia.org/wiki/File:KDE_1.0.jpg

https://en.wikipedia.org/wiki/File:KDE-2.0-es-es.png

The "wtf" era of KDE

https://en.wikipedia.org/wiki/File:Kde-3.2.3-es-es.png

https://en.wikipedia.org/wiki/File:KDE_4.png

The "we give up, just make it look like XFCE" era

https://en.wikipedia.org/wiki/File:KDE_5.2_Konqueror_and_Kon...