Note: if you are developer you should read the changelog more closely this time.
For core most notable change was that there is now language for contact which is used for example as printout and notification language. Also products is now in shipped mode by default. Product does not have primary category and shop product primary category should be only main category for product.
At admin we added mass actions for products, contacts and orders. We did some changes to form modifiers. Also we removed the language layer which caused way too many issues. The admin side got also multiple bug fixes for current features.
Front got app for showing recently viewed products. Option to login and register through checkout phases. Also the front we added multiple minor enhancements and bug fixes.
Update all translations and add support for Italian.
In case you have any questions about these features or you have hard time updating to latest version please contact us through forums or Gitter.
For the full list of changes see Change Log