As an X desktop you can run gnome, kde, xfce, xfwm, or really anything. Some components are Linux only (Xfce was recently bit by this) and thus may not work as expected or poorly if there is no abstraction layer that allows for us the use of devd(8) for example.
FreeBSD is my favourite OS for servers, it has good hardware support there where it matters most, and best of all is extremely stable. If Linux has met your needs so far, or even Windows, then stick with it. You won't find anything new and exciting and may even find it frustrating that certain things don't work as expected due to differences in API's that are available.
If you want a distribution of FreeBSD that is pretty well geared towards desktops, may I suggest taking a look at PC-BSD. They generally are not too far behind the official release of FreeBSD with their FreeBSD version, and it is an KDE environment that is easy to install.