Well there's something like over 700 bug fixes for starters, followed by an admin area theme browser as the main course served with new screen options for custom views the way you want them.
This is washed down with syntax highlighting in the code editor.
For dessert, try the new widget interface with the widget API addeded to the codex.
Freshly brewed and optimised javascript for vastly improved speed!
I must admit however, that I am only a recent convert to Wordpress. I've only created two sites with it so far, but I've been adding bookmarks to delicious on any nice wordpress articles I can find, with a view to reading them all to create my own "moonlighting" and self praise site! So watch this space.... now where am I going to find the time....