David Light has a great rundown of the new features over at his blog. There are some flashier improvements such as the ability to add ambient occlusion to a hidden line view (nice!) and some obvious, but long awaited improvements.
Tagging has been extended to allow you to Tag Rooms in linked
Architectural and MEP files. Spaces can be tagged in linked MEP files.
Keynoting tags now work across all linked file types whether they are
Architectural, MEP or Structural files. Area tagging now works on
linked Architectural and MEP models. The ability to Tag Rooms alone is
worth its weight in gold...
I'd have to agree that tagging rooms through linked models is worth the price of admission by itself, but I am also very excited about the UI improvements and the notion of assemblies. The example image David shows is of floors and walls that have multiple, independently identifiable and controllable layers. This has some really interesting implications and I'm curious to get my hands on it and see what can be done.