It's all subjective but I find that KDE apps need a lot of work in terms of control flow, UI hierarchy, white space usage. To me, these are some of the things that macOS and most third party applications for it get very much right, and coming from it KDE feels... jarring. In some ways it feels modern but in others I feel like I'm using Win9x, complete with overcrowded windows and dialog tunnels, with a new coat of paint. It would greatly benefit from someone sitting down and giving it all a rethink.

GNOME sits on the other side of the spectrum on these issues but I personally find it and in fact most GTK+ apps more aesthetically pleasing and more well organized even if all the buttons are too huge and its white space is like a football field.