I find KDE quite functional, although I do miss a couple features from OS X, particularly searchable menus, and being able to drag and drop a file into a dialog box and have it just select the file (going to the correct directory automatically).
#Gnome feels more like iOS to me, which is to say, a toy.
I can't speak to Platinum as a real user, though, as I only personally daily-drove 6.0.4 to 7.0.1 and Leopard to High Sierra.