KDE verions from 4.0 to 4.4 or so were very unstable. KDE 4.5 and later were rock solid. First versions of KDE 5 were very lacking. It's now back to rock solid

KDE verions from 4.0 to 4.4 or so were very unstable. KDE 4.5 and later were rock solid. First versions of KDE 5 were very lacking. It's now back to rock solid and much more visually pleasing and enjoyable to use than KDE 4. The Oxygen theme was very visually "heavy", its grey was quite depressing and overall did not look well. I would just get rid of it and switch to the Fusion theme. KDE 3 with its Plastik theme looked a bit more dated than Oxygen, but was way better. KDE 5's Breeze theme is perfect.