I have received my frogbeats C4 on thursday and I had been listening to them since friday and I have to say that the sound is amazing.
They are beautifully crafted just like all other owners had mentioned before 
I am not really an expert on headphones just had listened before to shure 420, sony ex1000, ath m50 and some bose I am still learning about sound signatures and to listen to the details but here are some early impresions
C4 have the best bass of all the headphones I have heard it is very well controlled and it does not interfere with the mids, you can feel it when the song requires it and you don't need to crack up the volume to hear it
The mids and the highs are very clear its just like I am comparing an old tv against an hd one when I go back to my old headphones the only one that kind of keeps the pase is the ex1000 but it sounds thinner like the sound is lower and you need to increase the volume to catch the same amount of details of the C4 and of course the highs on the ex1000 are harsher than the C4 and on the bass section there is no comparison the C4 is better than the ex1000.
One amazing thing I have noticed about the C4 is that they just show you the music like it is, I mean if you are listening a song that is cold the C4 will sound cold but if the next track is a warmer song it will sound warm ( perhaps this is the noobs way to explain neutral sound
)
A note on the bass, I am using an RSA SR-71B on single ended mode ( need to order the cable to test the balanced mode) so this could be affecting the bass performance since I have read on the forums that the RSA amps had very good bass.
And a question to the other owners that are out there, which is your favorite album to hear with the C4?