it's got lots of knobs and it's totally free! the HP filter signal gizmo in the top left corner is proabbly what i use the most. the envelope shape thing on the attack is pretty good too. the parallel feature works well. i don't understand what the mid scoop stuff does or the mode knob. but maybe i'll get there one day. it's definitely one of the most versatile and comprehensive compressors out there.
the only thing that bugs me is the limiter. the default setting is "pre" ie before the compression. not sure why that would be particularly useful. however even if you set it to "post" it doesn't seem to do what it's supposed to. at best it's wildly inaccurate. best turning it off.