KDE had a nice desktop, which I could never really love because my eyes disagreed too much with it, and no matter how much I tried, getting a consistent color/style/icon was difficult. After KDE 4.0, I simply gave up on it as a desktop environment.
> Still others consider KDE 4.0 as an example of how developers are divorced from the needs of end-users. However, as minor releases have gradually improved the user experience, most users seem to recognize the KDE 4 series as the accomplishment that it is.
I think most users that didn't leave KDE after KDE 4.[0-2] are probably happy with the improvements. Other users went somewhere else, and aren't looking back. Most people (read: me!) just want to get work done, and that normally happens within applications. For as long as the desktop gets out of the way and doesn't crash doing fancy graphic calls, it suffices.
Some KDE applications are IMO the best of the breed, such as Konsole and Yakuake. Digikam surely is capable (I've been using/trying photo managers a lot lately) but again it has an interface that I, personally, can't stand.
All in all, I think KDE's main contribution are its applications, and also the large number of special purpose small applications that, for one reason or another, always seem to appear first at KDE such as printing management, alarm, whatever-was-the-name-of-kde's gnome-do thing, and desktop wide password management. (apologies if I am wrong, but AFAIK all of those were KDE's 'firsts' and were later added to Gnome).