Pros: Natural Representation, Speed, Soundstage "Room-Feel Technology", Euphonic Midrange, Integrated Amplifier
Cons: Noise Cancelling Is not the best, very heavy, On-ear clamping pressure, plastic design, Slight grain in the treble, NC/Amplifier Noise
I've owned the Sennheiser Momentums, B&W P7's, Ultrasone Edition 8's, and other mid-fi portable headphones but I prefer these in terms of sound quality only.
Why? These headphone's have such an organic/balanced representation of all the sound frequencies that it really sounds accurate/natural opposed to accurate/cold or overly colored.
Sennheiser Momentum: Dull/bloated bass response, overly thick midrange, and recessed high frequencies.
B&W P7's: Unnatural Representation, slightly thin midrange, loose bass, strident high frequencies.
Ultasone Edition 8's: They are like $1499. Better than the P7's, but severely overpriced.
Bose QC 15: I tried to like them for their excellent noise cancellation but the sound is so horrible.
Sennheiser PXC 450- Dry, dry midrange, subpar bass response, better noise cancellation than the M4U2's but not better passive sound isolation.