Versions 4 and 5 look radically different.
Version 3 was fine. Very fine even for the time.
I didn't really like the default look of version 4. Oxygen had depressing colors, it lacked fineness. I always switched the theme to Fusion, or Cleanlooks, which imitated the Clearlooks GTK theme.
Version 5, with Breeze, is really good. Very elegant. By the way I also tend to find Gnome with the Breeze theme way nicer than with Adwaita (which is already fine).
The only DE I find almost as nice looking as Plasma with the default settings is macOS.
They are also constantly cleaning up the UI and making it simpler, bit by bit.
this is really funny, because to me, KDE starting from ~4 is the gaudiest thing I've seen.