I’ve been using KDE since my final migration to Linux operating system in 2005. It used to be useful, although ugly looking environment in its first versions.
KDE version 3 set the standard and KDE version 4 has improved over it. But including inclusion of the Plasma desktop instead of experimental SuperKaramba used previously has demonstrated itself as two-edged sword. Although nice and potentially likely highly useful, Plasma has been plagued by many problems. Crashes used to be frequent in the first versions of KDE 4 and rarely they still happen. Overall feeling from KDE is that it is not integrated well enough. Every program uses its own notifications, there are many different ways how a user is informed about an event etc. KDE also feels sometimes rather unresponsive or heavy.
I have recently tried using XFCE on a new desktop computer and it immediately felt lighter, faster and moreover, much better integrated. Everything seems to be well integrated in XFCE, icons, tooltips, pop-ups, notifications. Everything feels smooth and seamless.
KDE is now a giant slowly falling down under its own weight. I am really expecting what will the new version of KDE (number 5) bring.
Why I don’t mention Gnome? Because it’s way outdated, that’s why. And no, based on what I have seen, the Unity is not the right path to take either.