This one has one new feature.  If you create a MovieClip for your particle, there's a new rule which will randomly pick a frame in that MovieClip to use.

From the particle explorer, you just have to check off the box on the "intial" tab to get this functionality.

This lets you create a single effect with multiple particles very easily.

If you were using animated particles you could still do that by placing an animated movie clip on each frame of the main particle's movie clip.  Or don't check that box off and nothing changes.