This release of django CMS concentrates on usability and user-experience, by improving its responsiveness while performing editing operations, particularly those that involve updates to plugin trees.
Biggest changes of note:
* decoupling of the structure board from page rendering (you have to experience this to appreciate the difference it makes)
* decoupling of pages from the navigation node tree
Both bring significant speed advantages.
What's also new in 3.5
* page copy between sites
* better behaviour of the language chooser
* many bug-fixes
* ... and lots more!