You can check out all the features at Adobe.
I am most excited about the new JavaScript Engine for expressions and especially the ability to save your favorite expressions in a library!
And I am excited that the new Mocha included is a plug in instead of a stand alone application. I have not upgraded to the latest Mocha as it is a bit expensive, so am glad that this has been updated.
I am just hoping that this fixes some of the problems I have been having lately with UHD projects and not being able to open without either trashing my prefs (which also trashed my Workspaces) or importing the project into a fresh project which works until I have to re-open it. This has been incredibly frustrating!