To put it bluntly and simply, Samsung TouchWiz(TM) sucks. To me, a UI should be clean, simple, efficient, and it should follow the aesthetics of the phone itself. TouchWiz(TM) on the other hand is cluttered, inefficient, and ugly to look at. I will give Samsung some credit, the lock screen of the SGS3 is very beautiful, and
The SGS3 (White) has a cool but not cold color scheme, composed of mainly white and silver, along with the soft glow of the hardware keys.
TouchWiz(TM) on the other hand is compost of a strange color palette and the menues arranged in a way that it does not flow with the device itself, and I won't take the time to explain, but this Android Police review of the SGS3 pretty much sums up how I feel about TouchWiz(TM).
TouchWiz(TM) UI/UX sucks, therefore I will be redesigning it and posting my results in lots of pictures. Expect this to be a very long term project, you should see results, before the year is over. I hope. This will primarily apply to the SGS3 because it is the one I come in contact with the most.