As recently as a year ago, the Linux desktop was easy to describe. GNOME and KDE dominated, both offered an ecosystem of applications, and neither much different from Windows and OS X in their goals or design. Xfce was a distant third, with other desktop environments trailing even further behind.
Now, at the start of 2012, the state of the Linux desktop is radically altered. GNOME and KDE remain popular, but GNOME has been fragmented by the rise of Ubuntu's Unity shell.
Moreover, because of user dissatisfaction with GNOME and Unity, Xfce and other alternatives are receiving more consideration -- although how many users are switching to them remains almost entirely undocumented.
What the long term affects of these changes will be is impossible to predict. Whether user dissatisfaction will continue, and which desktop environments will gain popularity as a result is anybody's guess.
For now, the most you can say is that users of free and open source software have dropped the idea that a single desktop environment can suit everybody's needs.
Instead, most user's criterion for choosing a desktop fall into one of four main categories. In terms of appeal, desktop environments are either traditional, minimalist, experimental, or -- in a class by itself -- Unity.
Although some desktop environments could be squeezed into more than one category, the appeal of each of these types is usually quite distinct. For example, someone who prefers a minimalist environment is unlikely to consider an experimental one, any more than those who favor a traditional desktop will consider Unity. Generally, the appeal of these categories rarely overlaps
Traditional Desktop Environments
Traditional desktops are the conceptual descendants of Mac and Windows -- or, on the free desktop, the KDE 3 and GNOME 2 series. They feature a configurable panel, a main menu, and a general workspace, sometimes augmented by virtual work spaces. Some traditional desktop users may be conservative, but just as many seem to think of an interface as the launcher for their applications, and to want nothing more except some basic customization of themes and wallpaper.
By far the most popular traditional environment is Xfce. You often see it described on distribution mailing lists as a stripped down GNOME desktop. Since the development team is careful to control code bloat, most distribution's versions of Xfce are faster than their versions of GNOME or KDE.
However, because usability has become an equal priority in recent releases, to call Xfce minimalist no longer seems appropriate. Increasingly, it seems the alternative of choice for those who long for GNOME 2, including Linus Torvalds. Xfce's major weakness is that it has only a small ecosystem of applications, although its ability to run KDE and GNOME applications is carefully maintained.
In GNOME 3, you can also choose fallback mode, which looks like GNOME 2, but lacks panel applets and the ability to add application icons to the desktop. In Linux Mint (and, I suspect, in other distributions very shortly), you have the option of enabling Mint GNOME Shell Extensions (MGSE), whose combined effect is to replicate GNOME 2 within GNOME 3.
Modern KDE itself can be configured to be a traditional desktop if you make a Folder View your desktop and set it to display the Desktop folder in your home directory. However, to use KDE in this way is to ignore many of its features, and many GNOME users disgruntled about GNOME 3 and Unity are unlikely to consider KDE as an alternative.
Moreover, for those who preferred the KDE 3, a better choice is probably the Trinity Desktop Environment (TDE). TDE is an updated port of KDE 3. In fact, its version numbers are a continuation of KDE 3.x's. Because maintaining and updating the code is a huge effort, and the development team is small, TDE does suffer from more bugs than you may be used to. But, in general, TDE is an example of how, in free software, nothing is ever lost so long as someone is interested in preserving it.
Minimalist Desktop Environments
Minimalist interfaces have a long history in free software. To this day, you can still find long-time users who restrict themselves to a window manager like IceWM, or -- slightly more elaborately -- a tiled window manager like Ratpoison.
However, for many users, these choices are too extreme. Usually, the preference for a minimalist environment is a reaction to the size or lack of speed of GNOME or KDE (usually involving the word "bloated"), but that doesn't mean that their proponents want to give up all the convenience of a graphical interface. Some may be looking for an environment for older equipment, but most of those who favor minimalist environments simply seem to admire efficiency and simplicity over any other considerations.
One long-established minimalist choice that has undergone a minor revival in recent months is Enlightenment. Although originally described as a window manager, Enlightenment more closely resembles a lightweight desktop these days. It is highly configurable and generally stable, but users shopping around for an alternative might be put off by its slowness to reach a major release.
Instead, minimalist users seem to prefer more modern choices, such as LXDE, which promotes itself as a "fast-performing and energy-saving desktop environment." One sign of LXDE's popularity is that last year Lubuntu became an official variant of Ubuntu.
Another minimalist choice is Sugar, the interface for One Laptop Per Child. However, Sugar has had only limited acceptance as a general desktop environment. Its focus on children and education is not for everybody, and the interface, while simple to learn, may be too different for many users to seriously consider it.
The last year also saw the release of Razor-qt, whose home page summarizes it as "tailored for users who value simplicity, speed, and an intuitive interface."
If none of these choice suit your minimalist instincts, do a search on Distrowatch for distributions based on various desktop environments. The majority of options in the desktop environment field are for minimalist options -- proof, if any were needed, of how popular this criterion is.
Experimental Desktop Environments
Experimental desktops try to go beyond the traditional expectations and anticipate how users might work more efficiently. Although you can find many interesting experimental minor environments, to date, so far the major experimental desktops are GNOME and KDE.
It didn't use to be that way. For the first decade of their existence, both GNOME and KDE had the same goal: to catch up to existing proprietary desktop environments like Windows. Having reached that goal several years ago, both projects decided to try to get ahead of their proprietary rivals, and innovate.
Until then, for all the famous flame wars, GNOME and KDE were functionally similar. If one added a new feature, the other was quick to follow, and efforts such as freedesktop.org existed mainly to ensure mutual compatibility and cooperation.
But in KDE 4 and GNOME 3, the two most popular desktops presented dramatically different visions of the future of graphical interfaces.
Both abstracted the interface from the functional core, which allowed Unity to run on top of GNOME, and KDE to develop desktops for different hardware platforms. However, the results could hardly have been more different if deliberately chosen.
GNOME chose to eliminate clutter -- by which it meant features like panel applets and icons on the desktops. In their place, GNOME added an overview and made virtual desktops an automatic feature. Instead of accommodating different work flows, it enforced a particular one in the hopes of making everything simpler and more efficient.
By contrast, KDE focused on increasing the choices on the desktop. Instead of a single desktop, it encouraged multiple ones, each with its own configuration. Instead of a single set of widgets and icons, KDE offered multiple ones. Where GNOME eliminated applets, KDE allowed its widgets to spill over from the panel to the desktop.
These were radical changes, and direct causes of the present desktop environment fragmentation. Both were too much for traditionalists, and neither were major moves toward minimalism, especially KDE, whose fourth release series is generally considered slower than its third release series.
All the same, both these experiments have their supporters. Whether you appreciate one of them depends on whether you agree with their assumptions of how desktop environments should involve. Of the two, KDE is more tolerant of different ways of working, but even it is often condemned by traditionalists and minimalists as being more complicated than anyone wants.
A Unity of One
Amid the other desktop environments available today, Unity is an anomaly. It is not a traditional desktop, nor a minimalist one, and, far from being experimental, it is a simplification -- some might say an over-simplification.
Just as importantly, Unity is not a reaction to user demands, nor an attempt to evolve the desktop. So far as anyone outside of Canonical and Ubuntu's inner circles can judge, Unity appears to be largely the vision of one man: Mark Shuttleworth, who stepped down as Canonical CEO so he could focus on interface design.
The motivations driving Unity appear to be pragmatic ones, such as developing an interface suitable for a variety of hardware platforms, and borrowing features from OS X to fit a particular concept of usability. As much as Ubuntu's elaborate color choices, Unity brands Ubuntu as a distribution unlike any other.
Much of the dislike of Unity seems more political than functional. The new environment was a top priority for Canonical and Ubuntu, and many resented the reluctance to explain the reasons for design designs, and the perceived lack of community input.
Outside of Canonical employees and long-time Ubuntu enthusiasts, praise for Unity seems muted. Some seem to be waiting to see how Unity develops before making up their minds about it. Others seem indifferent to it, so long as they can launch their applications with a minimum of effort.
When users do praise Unity, they usually mention its simplicity. Some also like the fact that configuration tools are not immediately obvious, since most users only use them immediately after installing. In many ways, Unity seems to have managed the reduction of clutter to which GNOME 3 aspired but fell short of.
The New Status Quo
With the Linux desktop pulling in all these directions at once, a return to the days when one desktop fit every need seems unlikely. The days are probably gone forever when one environment was only a minor variant of the others.
In some ways, this state of affairs seems wasteful. With different priorities, desktops cannot cooperate as easily as they once did, and duplication of effort seems inevitable. Some might argue, too, that the increased number of choices will only confuse new users.
Still, the fragmentation has its points. A project with clearly defined goals may be able to satisfy users more than an environment that tries to be all things to all people. Also, for long-time users, the increased recognition of minor projects seems long overdue.
Even more importantly, the user revolts that created the fragmentation may, in the long term, teach free software developers to start paying attention to users. Except in the case of Unity, developers looking at the last year may come to appreciate that they have no authority to impose changes on their user base. If they try, someone else is likely to come along with an innovation like the Mint GNOME Shell Extensions and give users what they want.
In the end, the fragmentation on the desktop may not be completely ideal. Yet, when you consider the individualism that is such a core value in the community, it is hard to imagine events happening in any other way.
At any rate, no matter what its advantages or disadvantages, fragmentation has become the norm on the desktop. Like it or not, at the start of 2012, it is the new reality, and shows no signs of going away.