What's in Drupal 7? Most definitely an extremely friendly and Intuitive Admin Interface!
My first impressions of Drupal 7 as Drupal Admin:
1. Extremely friendly and Intuitive Admin interface!
2. More Trendy: Extensive use of Jquery, a very interactive design
3. Navigation: Multiple Navigation points
Improved and Multiple Navigation points like:
1. Tool Bar (The Admin menu in Drupal 6)
3. Shortcuts and
4. Contextual links!
5. Admin Interface with additional TAB interface
6. Use of Overlay to display information
7. Vertical tabs in the content edit interface
Some Key Functionality in Drupal 7 core:
1. Better media handling - Image filed and Image cache is in Core
2. Custom content types in core
3. WYSIWYG Editor
4. Better Performance
5. Better tools to structure/organize content
6. Basic Views like module
Also in Core implies all these will be maintained by the Core team and be available with Drupal releases!
1. Creating Drupal 7.x modules
2. Theming Drupal 6 and 7
3. Converting 6.x themes to 7.x
4. Converting 6.x modules to 7.x - Categorical
5. Menu path changes from 6.x to 7.x
6. A peek at Drupal 7 theme system changes