The image painting core has been rewritten, with a number of new options and the ability to save brushes. 3D texture painting has gained the tools and settings previously only available for 2D image painting, in addition to dramatic speed improvements.
The 3D texture paint mode now support all tools previously only available in 2D, with the exception of the clone tool.
Image painting in 3D is now much faster when painting large images. Note that to take advantage of this speed improvement, the image width and height must be a power of two, for example the typical 512x512, 1024x1024 and 2048x2048 image sizes.
Brushes can now be stored for later use, saved in .blend files or library linked from other .blend files. Note that brushes always have the fake user flag set, to prevent them from being deleted when reloading to file.
The brush spacing and timing has been recoded to result in more even brush strokes, and the airbrush option can now be used for all tools.
Blend modes Add, Subtract, Multiply, Lighten and Darken were added. When setting the blend mode to Add Alpha or Erase Alpha, transparency is painted in the image.
Textures can be used to define the brush shape and color. The colorband associated with a texture is a useful tool to define transparency and color in textures.
If you have a table pen with pressure sensitivity, toggle the small "P" button next to the opacity, size, falloff and spacing buttons to control these parameters using the pressure of the pen.
The Texture Paint section in the manual has a more in depth explanation of these brush settings.