Q: What changes will I see in Windows Server 2012 R2 Update 1?
A: You'll find Start Screen changes to Server 2012 R2 Update 1, and to Windows 8.1, but Update 1 brings more changes to Windows 8.1 than to Server 2012 R2. Those changes occur around the use of keyboard and mouse. Some changes also apply to Windows Server 2012 R2, such as the Start Screen Power and Search buttons, plus other changes if the Desktop Experience feature is installed.
The Internet Explorer 11 Enterprise Mode is present in addition to all other updates since the release of Server 2012 R2.
The only change to Server 2012 R2 server capability is around Active Directory Federation Services (AD FS). These changes are meant to improve compatibility with Azure Active Directory and Office 365, which allows signing in with an alternate login ID that's an attribute of the user in the on-premises Active Directory Domain Services environment.