Pros: Accurate sound, wonderful soundstage, perfect mids
Cons: Could use more bass, can bring out the worst in recordings, not very "fun"
Perfect headphones for most instruments and vocals, could be better for hard rock and metal. I've never been so immersed in music in my life than while listening to these. My Bottlehead Crack Amplifier definitely improved their energy and sound quality. I do find myself using treble boost on my ipod, however, and I feel like there could be more "fun" headphones out there. I will be searching for a more bass heavy headphone with a full bodied sound for my hard rock and bass-necessary tracks.
I also listen to hard rock and metal often (Dream Theater, Kamelot, etc.) and the 600s are my most enjoyable phones for these genres.