Moreover, Unity tends to enforce a single way of working. For instance, most applications open full screen unless their windows are so small that doing so would be ridiculous. Similarly, while you can add application launchers to the desktop, Unity's design conceals this ability. Customization options are also relatively limited, although more have been added with each release and a selection of plug-ins can extend them.
You may approve of such tendencies if Unity's way of doing things happens to be yours, but, if it isn't, you may soon feel so restricted that you wonder why you ever bothered leaving Windows.
Another consideration before using Unity is that, for all its simplicity, the desktop is also the testing lab for experiments in interface design approved by Ubuntu's founder Mark Shuttleworth. So far, the Head Up Display, an experiment in an alternative to traditional menus, is optional, but in a few years time using Unity could mean being a test subject when all you really want to do is get some work done. That could be fascinating, especially if you are a Ubuntu enthusiast, but it could also prove as distracting as an unreachable itch.
Until last year, Xfce's main appeal was its careful balance of usability and memory requirements. Then, with the exodus of disgruntled users from GNOME 3, Xfce became newly popular. According to one indication, it is now more popular than GNOME.
The reasons for this popularity are easy to understand. Using the same toolkit, Xfce feels half-familiar to GNOME 2 users. Even more importantly, like GNOME 2, it is a traditional desktop, immediately understandable and with few claims of being anything else. At the same time, it is faster than GNOME 3 or KDE, and its releases are generally far stabler than those of other desktops.
The only real limitation is that Xfce has never attracted more than a handful of applications specifically designed for it. However, Xfce does run both GNOME and KDE applications reliably -- which is more inter-connectiveness than GNOME and KDE have sometimes managed.
The same users who consider Cinnamon, Mate, or Trinity should also give Xfce a try. If a lightweight desktop is your goal, consider LXDE as well.
The conclusion that emerges most clearly from these descriptions is that no desktop is likely to please every user. However, those that come closest tend to be those that allow room for a variety of work habits and a reasonable amount of customization.
For a minority, a lightweight alternative is appealing, but most users seem to regard memory bloat the way they do taxes -- it is not the price that concerns them but what they get for the price. In other words, unless they are working on an older computer with limited resources, most users do not seem especially worried about the memory that a desktop requires, so long as they have features that allow them to work as they want.
Some users (and even more pundits) are distressed by the resulting variety of choices, pointing out that it is inefficient, and the same design problems must be solved separately many times. But, rather than worrying about fragmentation (a word I have used myself too many times), perhaps we should be appreciating the diversity. All the alternatives may not be ideal for free software as a whole, but individual users can appreciate the luxury of being able to shop for exactly what they want.