It is pretty and all, I will give it that. It tries so hard to please the eye that it would be easy to overlook its shortcomings. Alas, I cannot.
First of all, it tries so hard to look like the Windows interface, or at least the bastard offspring of Windows and OS X now with KDE 4 (not that it looks bad). This is where the problem is. It looks like it but when you expect it to act like it (or at least somewhat similar) it doesn’t.
For example, when you have Windows XP installed and you go get yourself a nice media keyboard it allows you to control the Volume, open up programs, put your computer to sleep if you accidentally hit that button and so on. It is very handy. The same thing goes for using it in Gnome which does not even try to resemble a Windows desktop. It is nice to not have to set up hotkeys to do this, or have to use your mouse to change the volume, you can just move your hand up (try to avoid hitting the sleep button) and turn up/down/off the volume, open a calculator or perhaps even an email program. There is probably a way to set it up in the kde control panel, but you should not have to these days it should be detected that it is sending the volume up command (I would even settle for something that noticed that you had attached a media keyboard and asked you if you wanted to set it up). I guess what annoyed me most was that I installed it along side my Ubuntu install which just recognized my media keyboard and I figured that it would do the same in KDE installed over a Ubuntu backend.
Another thing is the single click on an icon to open it up. That is just annoying, it may be more efficient, but if you don’t expect it (coming from OS X, Gnome or Windows you might not) it is one of the most annoying difficult to get used to default behaviours that there is (aside from not picking up multimedia keyboards).