This seems to be a major release that focuses on enterprises and organisations that are interested in geographic information systems (GIS) and mapping. The release comes with ArcGIS Pro, a new application that is part of the ArcGIS desktop suite. The release provides users a single application to work on 2D and 3D datasets, which makes this feature a key part of ArcGIS 10.3.
The ArcGIS server product now comes with a portal, that helps users to expand the functionality and usability of the product. This makes the on premises servers also to take advantage of the portal interface.
Another key feature is inclusion of 3D across the platform, not just in the desktop version of it. This means, you can use 3D maps and web scenes in browsers, which would also be rolled-out in to the apps during 2015.