MacOS X is an OK GUI, but Apple was more interested in re-using NeXT technology than continuing the UI metaphors that experts like Brendan Laurel and Bruce Togganazini established since 1984. As IBM found out with OS2; you can't design a good UI by committee, and OSX was designed by comittee.
That being said, it's my OS of preference for my Macintosh hardware. With BSD core, the MacOS has built-in tools for everything I need to do. Finally I can participate in any network environment without 3rd party tools.