I think all impression threads stay in defense mode when criticisms are presented, that is fairly normal human behavior. I am a big fan of the Nighthawks and it is frustrating when other folks don't hear and/or appreciate their virtues as much as I do.
There are a number of things at play here, the first being the range of subtleties that may or may not be intended in our descriptions. One person might say something sounds a bit on the warm side of neutral, others might say something like bloated bass or rolled off treble, they might be hearing close to the same thing, but after their choice of words and the readers choice to interpret, the range of perception can be dramatically bigger than anything measurable or generally accepted as true.
I find some comments to be over the top, beyond the generally acceptable range of accounting for how we all hear things a little different, so I think it is fair to push back.
I try to be open and respect every opinion, and I try to be honest about my own bias. While headphones are a relatively new hobby for me, music is not, and after many many years of seeking out music performance, home and pro studios, music appreciation, musicianship (I mostly suck) and home audiophile pursuits, I do have confidence in my grounding on the basics.
As open as I try to be, I do have strong suspicions about the general population and even the specialized population here on Head-fi.org. First of all there is the clear difference in playback chain, music genre, and particular music preferences that we use to judge any single component, and that puts a very different, very narrow focus on our criteria and judgement. There is also the notion of presence and detail. This has been an issue in the home speaker audiophile world for a very long time. Things that impress upon first listen tend to not be accurate and "first listen" can last a fairly long time. I am convinced the industry is mostly cheating us with boosted presence regions, saturated/overloaded distortion artifacts and an engineering practice of sacrificing bass (and sometimes treble) to achieve the preferred "first listening preference" that they think will sell headphones the most.
The Nighthawk is not a bass-head headphone, so let's make that clear to everyone reading here that has not had a chance to hear a properly broken in example. Depending on any number of source/chain variables, it is almost as fair to say that they are not neutral in the bass either, but by how much over how broad a spectrum of the bass range (25-250 Hertz is my own definition here) is up for debate and how much is dependent on fit, seal, ear shape and angle, air volume, etc... is anyone's guess. My guess is that they are plus 3-4 dB at best in the 60-150 Hz range and that means "just barely noticeable" in my book. They are not anywhere close to the boosted bass I hear in an M100, MDR-1a, or even an ATH-M50x. So for those of us who are sensitive to boosted presence and distorted treble (even pleasant distortions) and just tired of music sounding thin instead of full bodied, the Nighthawk is a most welcome relief. So are things recessed or rolled off or missing or wonky as I move up in frequency to mids and treble? Not for me and not at all... Just because it is not longer boosted, or unusually present or highlighted in some way does not mean it is still not there in much the same way I would expect it in a live performance, in a studio or coming through a set of speakers in a room. It is all still there, I can hear it quite clearly. I can hear the layers of sound and microphone types and techniques in vocal performances, I can hear the room and the instrumental tone and decay, I can hear reverb trails and a sense of space. I have and love the sound of the HD600, but they are not comfortable for me beyond 20-30 minutes of use so I am selling them. They have a nice midrange, but in some cases it can sound a bit veiled, in other cases a bit euphonic, and in most cases I find them lacking at the frequency extremes and some harshness across the band at louder volumes. They don't always have the degree of punch I expect with certain recordings but on the plus side they can be rather polite with recordings that have questionable sonics IMHO. The Nighthawks are most definitely in the same class as far as I am concerned in that they, more so than the vast majority of products in this industry, have attempted to be truthful to the source and intersect the values of a musician, recording professional, music fan and audiophile without selling out to the potential "first impression" weakness of any one of them. To accomplish this, or perhaps just come somewhat close to this, at such a light physical weight and with such a comfortable design, for a first effort from a new brand in this vertical... let's just say I would not want to be a designer/engineer/product manager at any other headphone company walking around knowing that the Nighthawk could get put up in my face if my employer wanted an honest, natural sounding headphone regardless of how many sheeple would throw down their dollars and walk out of the store with them.