A recent upgrade to openSUSE 11.1 afforded me the opportunity to give KDE4 a try again. I'm a long-time fan of KDE3 and was hoping for pleasant surprises. I got half my wish. KDE4 may be a bit prettier in places (but not the fonts), but it's neither as consistent or as usable as KDE3 was. It's certainly not as stable or as fast (even with desktop effects turned off), and there have been a bunch of non-obvious changes. To me, it feels like a couple of steps backwards in experience and utility.
In particular, konsole is a BIG step backwards - if you open up a konsole with a given command (like ssh SOMEHOST), then new tabs will *also* execute that command (something KDE3's konsole did not do - quite logically). If you hit the "close tab" button (which I to root around in preferences to find) konsole hangs and has to be killed. Sweet! There are a fraction of the preferences available, some things I found quite useful are now gone.
Replacing konqueror with dolphin as the default file browser was not a step forward, either. The inability to right-click on a menu item (in an application menu) and add it to the bar was removed - so how do I add firefox, konsole, and the 2 or 3 other apps I open up 400 times a day? It's not clear to me and if it's not clear to me then, IMO, it's a step backwards. How do I configure my desktops so I can easily mouse between them by dragging windows or even just moving my cursors across the edges? I don't see it anywhere!
So far, KDE4 has removed features I use, added ones I find annoying, hurt stability and speed, and impeded my workflow. I'm sure there are good reasons for KDE4, especially architectural ones, but so far my experience does not bear out any advantage, and some significant disadvantages.
You may say to yourself, "you just have to know where to look" but if I wanted that sort of opaqueness I'd run GNOME, or at least older versions of GNOME - maybe they've improved some. KDE3 was a very *usable*, *stable* desktop environment and so far KDE4 is worse in nearly every aspect I care about. It's too bad because I know a great deal of work has gone into it, but I'm really beginning to wonder if that work has been with the right goals and priority management in mind.