First, did you compile Tk yourself ( which is quite easy ) or are you using what is provided by the Mac? Try compiling it yourself and report any errors. Don't worry about the test suite failing.

As far as Tk looking really bad, really 90's, it is really 90's. :-) You have to understand the simplicity of the Tk toolkit in order to fully appreciate it. It requires nothing more the basic X system libs to compile and run. It itself, is quite a small codebase, which in this age of security concerns has many advantages. With Tk, you can make your widgets as fancy as you want, and even make make your own custom subclassed widgets simply out the Canvas widget. See Tk-CanvasDirTree for a simple example. True you have to put alot extra color statements to get the effect you desire, and Tk dosn't conform to any theme standards, like Gtk2 or Gtk3. Then again, Gtk2 and Gtk3 will load an enormous amount of libraries .... which do your prefer? Theme conforming modern looking GUI's which come a load of dependencies, or the basic simplicity of Tk? Your choice.

If you want to make something really special with Tk, including semi-transparency, and matrice geometry control, like zooming and rotations, see Tk::Zinc