To be sure, KDE has made many improvements since the last time I complained about its shortcomings, in 2008.
That last commentary was made when the current release was 4.0, which its developers never intended for general use. In the five releases since then, several of my complaints have been eliminated or made less urgent by the addition of more panel options and widgets, and some improved wording of items on the interface. Accessibility options have also improved, mainly through the desktop effects, although KDE still lags behind GNOME in this area.
However, new features and my own growing familiarity with KDE mean that there are still improvements that I would like to see. Here are the seven top improvements I would suggest for KDE:
The Desktop Toolkit is the small widget that sits on the upper right on the edge of the screen. Originally shaped like a cashew, it now looks like a tab. Click on it, and you find all sorts of useful tools: Add Widgets, Add Activity, Lock Widgets, and others. However, some users never seem to have looked at it, considering that Fedora has a package called kde-plasma-ihatethecashew whose sole purpose is to remove it.
What people have noticed is that the Desktop Toolkit gets in the way. Place a panel at the top of the screen, and it overlays the similarly shaped panel customization button so that you can never be sure what you are clicking.
You can drag the cashew to some other place (mine is on the bottom left), but many people haven't noticed that, either. At any rate, no matter where you place it, the Toolkit looks like a menu, but doesn't close when you click elsewhere on the desktop; instead, you have to click on the button again.
The time seems overdue to admit that the Toolkit is an idea that has failed. Its functions could be demoted to a menu, a panel widget, a context menu, or anywhere else they would be more noticeable.
KDE 4 introduced Activities, a kind of improved Virtual Desktop, each of which can have different icons and containments (layouts). These are welcome additions, but, for no apparent reason, a widget for Virtual Desktops still exists.
Perhaps this duplication of function was intended to minimize confusion amid all the changes in KDE 4. However, if the users I've heard talking are typical, what the duplication actually does is create uncertainty about which function to use. Since Virtual Desktops are at least familiar, many people end up using them and not taking advantage of the improvements offered by Activities. Possibly, future development plans justify the duplication, but, from a user's perspective, nowadays it seems to create more confusion than it resolves.
System Settings is the software and hardware configuration dialog for KDE. Its problem is that, in five releases, the KDE 4 series has yet to settle on a standard layout within the dialog. The changes aren't minor, either -- between releases, top level items have been demoted, and lower items promoted, and the names of categories and items have changed, all of which can make finding a particular feature time-consuming after you've upgraded.
KDE 4.5, the latest release, offers some hope in the fact that it finally eliminated the Advanced tab for System Settings, which in earlier releases was a dumping ground for configuration items that didn't fit anywhere else. But whether users can hope that existing items will stay where they are for two consecutive releases remains to be seen.
Yes, I know that you change the panel's background color by changing the Desktop Theme. But I suspect that most users will look for this item by right-clicking the desktop and choosing Panel Options -> Panel Settings, because that's where the other panel configuration choices are found. To the extent that users are aware that they need to go to System Settings, they are only going to be peeved at the extra fumbling about.
And while changes are being made, why not add options to add an image or texture to the panel?