You mean other than the crazy new user interface? Quite a bit, but
there's not much that will affect the average single purpose web server.
Most enhancements so far have been geared towards cloud servers and
management of cloud servers in a much more integrated and intuitive way.
That said, some things to note:
IIS 8
The new IIS is more robust but the new UI shouldn't throw anyone for a loop.
ASP.NET 4.5
If you're looking to switch you're application pool to 4.5 you
won't find the option, however its active and running on your 4.0
application pool already so feel free to play around!
New Graphical User Interface (GUI)
As mentioned, the design is simplistic in style and similar to
what was going on with Windows Phone. Formerly known as Metro, now
called Modern, the GUI has some up in arms but once you get used to it,
it seems to work quite well.
New Start Menu
No start menu button
New search features (search files/apps and settings separately)
Categories 
