I am planning to do a better review of the GH2 soon, however, I can start with a mini-review first.
After 100 hours of breaking into the Grado GH2 in my Audio GD NFB-12.1 Dual WM8781 Amp/DAC and my newly arrived FiiO X5 3rd Gen with the A5 Portable Amp, I can say that the GH2 has taken Grado into a different direction of sound, which I liked very much. I was very disappointed on the early run RS1e (no bass, not the biggest fan of the highs) when compared to the RS1i that I owned in the past. The GH2 to me was what I was hopping for when I purchased the RS1e a few years ago.
Some of the points of the sound of the GH2:
*The Highs are tamed, it is like they adjusted it slightly so it doesn't sound too hot on the top.
*The Mids are still Grado, Forwarded Mids with a little more soundstage, but it seems like you are sitting in the third row (where with Grados I feel like I am sitting in the first row). Could be veiled, but I kind-of like that sound.
*The Lows are actually there with this Grado. More low-end response from the RS1e and my current cheap SR225e pair. This helps with tracks where you are focusing on the bass guitar or even electronic music beats. However, bass-heads will still be disappointed since the GH2 won't overpower you with low end. While I like more low end with my music, too much of it hurts my ears.
All in all, I found the GH2 to be a very smooth headphone, with the highs tamed a bit and better low end response. I'll have more details on another date.