I used ACID for a few weeks since it was initially released for Gnome Shell 3.4, and I absolutely loved it for its boldness and its unique and successful combination of unambiguous clean borders, and optical functionality.
I am more than happy to see that theRealPadster decided to update his theme, providing a new version that now supports Gnome Shell 3.6 too!
The colors used, combined with the usage of definite borders provide a clean and modern theme that is very easy to your brain and quite friendly to your eyes too. The switches are completely color based and transparencies are only found on the view applications screen.
The changelog for this second version of this magnificent theme include a general restructure, increase checkboxes by 2px, some bug fixes, better looking submenus and smaller Rhythmbox notification control buttons.