A highly flexible, easy to use verb that can easily become your bread and butter. The FabFilter team really understand how to design a UI and to me, this is the real key to their success. It takes literally seconds to design the perfect space. Whether you're focused on reflections or tail, tiny or huge, subtle or slammed, this verb does it all and does it well. If stuck on a desert island with only a single verb, you'd be smart to choose Pro-R.
Be sure to check out the whole FabFilter product line. These plugins are absolute tops.