It’s gaining polish with every point release. Desktop search is finally quick. The UI stack (QML) is nimble and powerful. Breeze is the best looking flat design, both beautiful and clean. Even the default desktop wallpapers are gorgeous.
The only thing remaining is the Akonadi legacy, which is being replaced. The rest is details. KDE is the best desktop Linux has to offer now, and it’s the best platform to build upon in the future.
I tried to like KDE, but every time I tried it, one of the first apps I tried would immediately crash. Plus it's default looked like a bad copy of Windows XP, which was a bad copy of the Mac, so it looked really bad. (That was a long time ago.) Unfortunately, GNOME looked nice, but had no features, so I just gave up and went to a bare window manager and realized I have no need for anything a DE offers. Then the problem became that sawfish became unsupported, and nothing else had the same customizability.