I bought a Galaxy S3 (Android 4).
I downloaded the user manual, and I can't find a way to change the appearance. I can change the wallpaper and the font size, but I can't change drawer transition behavior, the general UI theme or the icon set.
Download Apex launcher--
It has full support for themes and transitions, icons, etc-
For Icon packs, "ADW Icons" is a good keyword to use- since Apex will use ADW icons.