One thing that annoys me is the Ribbon won't stay minimized. In Outlook 2010 there is a Minimize Ribbon option you can checkmark in the quick access toolbar to hide it until you want it. That option is now missing. I have outlook setup to open the next item when I delete an open email. I close the ribbon, delete the email, and bam, it open again when the next email is displayed. Outlook 2010 didn't do this. 99% of the time all I need is the quick access toolbar so the open ribbon is just wasting screen space.