I do not want to sound like a Audez'e fanboy (but I guess I have become already because the sound is so authentic that I cannot help myself)...
But the bass on Rev2 is extremely defined, accurate, TOTALLY NEUTRAL and fluent. The bass guitar you will get with rock and metal is simply stunning, live performances are also so real because of bass frequencies strongly influencing the overall ambience in the natural way.
Mids are very very nice, from pop rock to symphonic metal, male vocals sound extremely authentic and female vocals do not have any sense of glare (that's of course influenced by a bit lowered lower highs). They are also ruler-flat but I don't think there is any sort of WOW moment involved - just natural and defined. I can understand that someone could find them too full as they are not overpowered by overtreble as it is usual with the majority of phones.
I find the treble extraordinary good... The treble is the main reason why I am not interested in any other brand, Hifiman included. There so much texture involved! Does not matter if you like pop, rock or metal, the texture and balance is just... fenomenal. I personally do not understand how anyone can recommend Grado for metal. I would recommend Audeze for metal over anything I can ever imagine. It's a bit lowered in the region of 3 - 9 khz where it is desired with non-top-recorded music in order to get rid of distraction from audible artifacts in your music, and/or to keep the treble allright/not too forward/in balance with the rest of the frequency spectrum.
The phone works pretty well with acoustic-guitar based music as well... But I guess that for purely acoustic music listeners, there are phones that could do the job better (read - in a more exciting way) for them.
Transparency is what makes their sound to be very life-like... They do not sound like a pair of headphones to me, they are rather like a window to the room or hall where the music is being performed.
As I said before, soundstage seekers are not going to be satisfied... But I use TB Isone in order to get the speaker-like interpretation. For professional purposes, you have perfect bass and mids - you just need to correct the treble a bit according to the graph you receive. I would say a perfect pair of headphones for 1000USD.