This has probably been my go to filter fx plugin for a while now. It's definitely one of the best I've tried. But there's still a lot to be desired.
Good modulation, the envelope follower is pretty solid, although I never use it. The LFO is not necessarily standard, it has some idiosyncrasies, for example you need to use the "balance" control to create a saw but it won't show that on the graph if you do so. You can however trigger the LFO by sending it MIDI which means effectively you can add this onto a synth that doesn't have a complex filter, and send it the same MIDI signal. It's good for dubstep wobbles. If you animate a filter sweep in your track (ie with your daw) you actually get to see the filter move up and down. I don't know but this works for me. Unfortunately the LFOs etc don't make the filters move that would be a nice optional extra.
Why are there only bit pass, LP and HP options? It would be great to get a decent band pass with a variable width, a notch and a bell would be pretty great. Why did they stop at just three filter types? Also there needs to be an optional oversample. At the most extreme values you can hear aliasing on this plug and that's a big design faux-pas. Also what do the different filter "types" actually do? They seem to vary Q values and saturation levels but it would be nice if the instruction pdf or help box actually went into more detail on this. My final criticism is an obvious one: wayyyy too expensive. There are plenty of similiar plugs that go for around a third of the price. (Few have quite as many features as volcano however).