Last time I checked, OS X did not let you replace the main window system or the OS status bar. The theme of the interface is also not as easily changeable as a KDE or GTK+ theme.

If there's a way to completely remove the graphical interface, it's definitely harder than in Linux, and not as usable afterwards.

You might argue that these options are not needed for a typical OS X user, and perhaps you're right. But you cannot say it really gives you "full control of the system".