Many people complain that KDE contains horrible amount of bugs, but it also contain awesome amount of practical functionality that other environments miss and it seems to me that most of the bugs are in applications like Amarok and luckily not in the core systems (ie. Plasma, KWin) since ~4.6.
KWin and its setting dialogs are just wonderful since KDE 3.5. I've never managed to find ALT+<rightclick | leftclick> behavior settings in Gnome (I like ALT windows resizing and use no window borders.) and things like setting if ALT-TAB cycle windows from all desktops or just one desktop.
Many also curse dolphin IMHO, but changing default file browser works like charm and i.e. I love dolphin, it's simple, tabbed, can be very conveniently controlled entirely by keyboard, feature combined button/editable addressbar (This can't be found in Nautilus or Thunar) and supports treeview. Btw. one can turn of those side panels or even menu+toolbars of course.