Release Notes: This release has a completely new Media Library manager, easier-than-ever image galleries, and a new mobile-first, responsive theme named TwentyTwelve. There are also improvements to multi-site functionality, a retina-ready admin, and many new-and-improved API changes for developers.
Release Notes: Major work was done on the TinyMCE WYSIWYG editor, creating a custom schema to adhere to the HTML5 living standard. It should now handle unusual OBJECT/EMBED situations, among other things.
Release Notes: Final UI improvements to the media manager. Better reporting for upload errors. Improvements for mobile, IE, and RTL languages. A cookie fix for sub-domain multi-site when installed in a sub-folder.
Release Notes: This will probably be the final release candidate before the official release of WordPress 3.5. This version has a completely new media library, Dashboard streamlining, new performance enhancements for Multisite, the ability to enable Multisite when installed in a subdirectory of the document root, and other features and enhancements.