Another reason why KDE has weathered protests better than other desktops is that, whenever possible, it has allowed users a choice of whether to use an innovation. If you don't like System Settings presented as icons, you can use a tree view similar to the one in the KDE 3 series. If you don't like the default menu, you can use the classic menu or the Lancelot widget. If you're baffled by Activities, you can stick to Virtual Desktops instead, and get much the same results by changing a setting or two.
All of these fallbacks are fully functional, too -- in marked contrast to GNOME's fallback mode, which is a crippled imitation of the GNOME 2 series. Many details of the KDE 3 release series are rearranged or renamed in the latest versions, but the major features, at least, are available if you take the time to explore.
Anyone who follows the development of GNOME 3 or Unity can't help but notice how often the jargon of usability design is tossed around. On both development teams, usability studies are evoked as an authority, intended to stifle criticism.
Consequently, as anyone with experience can tell you, success in applying usability principles is highly dependent on your basic principles. In other words, you can easily create an interface whose every feature is in accord with the latest research in usability and still have flawed results because it ignores context and audience. Despite strenuous efforts to raise usability to scientific respectability, interface design stubbornly remains as much an art as a collection of established principles.
Both Unity and the GNOME 3 series are designed with the assumption that there is one optimal way to work. Unity, for example, allows files to be added to the desktop, while applications go on the launcher. Similarly, GNOME 3 assumes that all users want virtual desktops, and automatically creates them -- regardless of whether you want them or not.
These ideas have a certain logic behind them, and some users do appreciate them. But what about the users who want easy access to more applications than the dozen or so that the launcher can absorb before it becomes unusable? Or the users who find virtual desktops confusing? These users aren't going to appreciate being forced to work in a way that makes them uncomfortable, no matter how much logic you muster against them. Custom trumps usability, every time.
Today, Linux interface design seems centered largely on new users. In Unity's case, this emphasis is probably partially due to Canonical's march to profitability and its hope of attracting users from other platforms. However, other development teams have also adopted it, usually in the name of not frightening newcomers away.
One result of this emphasis is interfaces that are simple to learn for anyone who has ever used a desktop environment. Unfortunately, though, another result is interfaces that advanced users are likely to find frustrating.
In particular, in both Unity and the GNOME 3 series, reaching configuration options, or even a command line, requires a far longer descent into the menus than with in other interfaces. Advanced users can, of course, customize the interfaces so the features they want are more accessible, but this is still an inconvenience that GNOME 2 or KDE don't share.