The changes to the Drupal 7 Theme layer aren’t revolutionary, but there are so many improvements, you may have trouble… ah… controlling yourself.
- Crappy-themes-be-gone™
- Template cleanup
- Numerous name changes (like sidebars and menus)
- phptemplate_ prefix is gone
- $classes and $classes_array
- theme functions and preprocess functions
- More regions, less hard-coded page variables
- Holy crap, content is now a block!
- template suggestion wildcard
- JQuery UI
- Granular theming
- html.tpl.php
- hook_page_alter()