I do hope I'm not to late, but I wanted to skim the articles to at least get a sense of what others were saying.
So far, what I would say is important to me? I would say:
1. linearity and balance
2. tonal behavior (Not just "balance"; transient response, texture, and control)
3. Build quality (Comfort, durability, and aesthetics)
Linearity: quick changes in efficiency between octaves is really distracting, and can become very obvious in orchestral music. Between that and soundstage (not real important to me), it killed my enjoyment of the Sony MDR-V6's. Meanwhile, the V6's were fairly even across the whole range, but had jarring transitions between, and even inside of, octaves. I haven't really had the opportunity to listen to a purely even set of headphones, but I do like a little bit of coloration. A bit of of elevated bass is nice, since you don't get the physical feedback from the bass of large speakers, and I do like a little bit of treble flamboyance. However, I would rather those colorations be very minor than detract an iota from the next category.
Tonal Behavior: I love the bass (the instrument), both acoustic and electric, and I hate when the bass (the collection of frequencies) is loose, and the character of that wonderful instrument is lost. Meanwhile, the same speaks for the guitar, the violin, or even the piccolo or flute: most people don't notice the absence of the rasp of bow on string, the clicking of keys, or intake of breath. What they notice is when complex sections lose their players, and just become a tonal mass. That is not to say that I don't delight in hearing that extra bit of detail on a good headphone, it's just not the details that suffer most on a transientially insensitive 'phone, it's the sense of immersion and totallity to the sound.
Build quality: it's bloody obvious, just do it. I don't really care for light headphones, and I would rather that they exude solidity. Mind you, a bar of titanium isn't necessary, you can do it with plastics, excepting the articulation in joints. If they are plastic, they need to be thick plastic. Comfort? Thick squishy pads are nice and all, but a less sweaty option would be something that Bose did right with the Triports: thin, memory-foam pads, that were flanged inwards. The cup was barely bigger than your ear, but the space inside the earpad was larger than the inner dimension of the pad (does that make sense?). This allowed for a very thermally permeable cup, that was still quite comfortable.
--Edit-- I do like the styling of the full-size Phiaton headphones; they do look very clean and professional, with just enough flair. But, excuse me, but what is "electrodynamic" supposed to mean? Is it just a cheesy way to make it seem like the MS series driver is something special, or is actually something different?