Here's some of the highlights for this release.
|LightDM with Unity greeter|
|The new default email client for Ubuntu comes with complementary indicator support|
|Deja Dup backup now comes with every Ubuntu install|
|Indicator menus got a refresh. Both session-indicator and me-menu seems to have changed|
There's more, of course, including an updated kernel, multiarch support, a new alt-tab switcher, Gnome 3, and many others. Unity 2D is now the official fallback solution for hardware without 3D acceleration driver support.
As always, be sure to check out the list of known issues for anything that might affect your particular configuration. More details on the release are available from the technical overview page.