Blender 2.73 brings a lot of new features. One of them is the overhaul of the Grease Pencil tool.
Here is a list of the most notable changes:
- You can now animate with the Grease Pencil tool
- A Sequencer Backdrop, -similar to the one on the compositor-, was added and Cycles got various improvements!
- Cycles now supports GeForce 9xx GPUs.
- Improved rendering with Area Lights in Cycles.
- New fullscreen mode without buttons or any other bothering elements to improve the UI.
- 3D Viewport got an option to display the world background.
- Confirm Threshold to confirm a pie menu without releasing the original key.
- Nested Pie Menus (which is a Pie Menu within a Pie Menu) are now supported.
- Knife tool: Cuts can now be created using free-hand drawing and cut-loops can be closed with a double-click.
- New selection method: “Select Similar Regions”
- Freestyle got a new SVG exporter in the form of an add-on.
- Various bug fixes.
For a more detailed list, you can find the release notes here