I don't normally get blown away by pedals, but this certainly did it for me. If I had to describe it in one sentence, it would simply be "Buy this pedal" The Boss RV-3 is a highly sought after pedal in the reverb world, the RV-6 trumps it in my opinion.
The modulation setting sounds good, no complaints there. I'm not a big spring,room, or hall user, so I can't really comment on them. The dynamic setting is also an interesting one but one I don't tend to use. Where this pedal really shines for me is in its first two settings, +delay, and Shimmer. The +delay mode does exactly what you'd expect it to. It adds a delay line to your reverb, with the kind of quality delay you'd expect from Boss. If you have room for only one delay on your board, this setting can be very useful for ambient swells and such.
Where this pedal really shines is it's shimmer setting. Shimmer seems to be the in thing when it comes to reverb these days and the RV-6 beats them all for me. You can control the tone of the shimmer, clockwise gives you the classic octave up setting you'd be used to, but further counterclockwise settings give the shimmer this choir like heavenly sound that I just can't get enough of. It's this shaping of the shimmer tone (not to mention the incredible sound) that makes the RV-6 the best ambient reverb on the market at the minute.
I also have to mention Thomann shipped this pedal to me on a Friday, it arrived at my door in Dublin at 7am on Tuesday. That's 1 full working day to get from their warehouse to my door on the other side of Europe. Phenomenal service, for a phenomenal pedal at a phenomenal price.