Exchange Server 2013 comes with a number of new features as well as improvements on existing features that are already familiar to those who have worked with Exchange Server 2010.
Here are a few of the highlights:
Reduction in server roles to just two; Client Access server and Mailbox server
New streamlined Outlook 2013 and Outlook Web App user interfaces, and offline access for OWA
No more Exchange Management Console, all administration is now performed using the new web-based Exchange Administration Center and the Exchange Management Shell (using PowerShell 3.0)
Improvements to high availability features and manageability
Public folders are now stored in mailbox databases and can take advantage of Database Availability Groups for replication and high availability
Data loss prevention capabilities that can be integrated into Transport Rules