I should excuse myself for my verdict of the Mathematica GUI on Windows. You should know, that I am a design freak. It is not my fault that I use Windows. I have to.
I now saw the Mac version on a modern system. The interface does indeed look and work a lot better. Here is a screen dump I found in the net. The resolution is a bit low. If anyone can provide me with a modern version, I will update this.
This is much better than what I saw on my system.
Good design is clear design. Some people seem to prefer a wild design with lot of details. Maybe they get the impression that a software of this kind has a lot of features. I think this is childish.
For comparison, I add a screen dump of an older version of Mathematica on Windows. I found it on the Heise pages. It is so ugly!