NightHawks remain the quirkiest headphones in this hobby. They definitely do something special, but don't fit any standards.
Changing from any other headphones to the NightHawk from similar or higher category can easily be a disappointment. Coming from lower categories the experience is more likely to be positive.
The NightHawk really shows what it can do if you listen to them exclusively and ignore all other headphones for quite a while.
The biggest advantage of NigtHawk is the exceptional comfort and fatigue free sound. The sound is also organic and rich. Soundstage is a bit small, or let's call it 'intimate'.
Once you try higher rated and more popular (and more expensive) headphones, the NightHawk's shortcomings become more obvious. The sound is not very well balanced. All dynamic headphones have some level of a mid-bass hump, but on the NHs this hump is pretty enormous. Fun for certain genres, but not very natural. Treble also lacks some shimmer and spaciousness. I know AQ's marketing about the NHs treble, and to a certain degree it is true but not completely true. It is not that the NH's treble is the only 'right' treble and everything else is wrong. More like it is one interesting approach of treble presentation, but far from perfect. Compared to something like the LCD2 or Focal Clear, NH's treble sounds like the instruments were toys instead of real ones. Expecially the percussion. On the two fore-mentioned headphones percussion sounds real, airy and the shimmering sound of the cymbals float around. On the NH in comparison drums and percussion almost sound like when my 5 year old nephew is hitting his plastic drum set.
NightHawk requires exclusivity. When you only listen to the NHs for a long period of time, they give you something really special. Technically not necessarily right from an audio perspective, far from neutral, but a special flavour. For this unique flavour I can see why people keep them. But I don't think they will become a classic like the Sennheiser HD6X0 models or the LCD2 for example.
I loved my NightHawks for a long time, but I was listening to them almost exclusively. I liked the warm, fatigue-free sound and comfort. My LCD2C has a much more balanced and accurate sound. Still warmish and smooth, but much clearer and much more balanced. Linear bass response down to 20Hz. I actually rebought the NH for sentimental reasons, but sold again since the LCD2C has much superior sound quality overall. I could have kept the NH for fun but I didn't.
Finally let me leave here something encouraging:
As most of us know AQ pretty much said these headphones are discontinued.
Let me just copy here my comment on an AQ post on another platform and their reply:
Me: - It is a shame you decided to discontinue them.
AQ: - It's much too soon to say with certainty, but the possibility remains that we'll release a variation of NightHawk/NightOwl at some point in the future. We shall see!