Things such as...
*. Enhanced Remote Desktop support via SFTP, SMB, FTP, etc are updated
*. Older features such as ThunarVFS, HAL, udev, etc are dropped (well portions of them of course).
*. Complete re-written application panel
*. New menu plugin
*. Enhanced settings editor
Now these are just the main one but other things like new wallpapers, look n feel, etc are also embedded. If you want to try it out then the best way will be using a Linux distro that currently ships it or upgrading from the older one rather than getting the source code to build it from the scratch.