So, now that I have had some time with the Nighthawks I have a better idea of whether they are keepers. Hey, I knew I would like them because I spent a few hours comparing them with several other headphones before picking them up. However, I had no idea how much I would like them. So, in short here is the skinny:
Construction: very good. Very little plastic. These will hold up over the long term.
Comfort: very good. The are light enough and fit your head comfortably. No issues here and are good for long listening sessions.
Sound: deep and well articulate bass. Favors the low end but not at a cost of timbre. They have truth to instruments with a fairly balanced but rich frequency response. Maybe, slightly rolled off up top, which could be boosted 1.5 or so db's starting at around 14000hz but satisfying none the less.
Engagement: these cans are a bit addicting and can be somewhat hard to take off.
Value: at $699 they run with others in that price range. At $399 they are a real bargain and well worth buying as a secondary pair of cans.
Other:for open cans they really do a decent job of keeping out external sound. They are much better in this area than other open eared cans. This was a nice added surprise.
In the end, I will be keeping my Nighthawks and they will most like be in my regular rotation with my Hifiman 560. The 560s have a wider soundstage and better high frequencies. The rest is about a tie with the exception of the low end, which due to the rich sound of the Nighthawaks gives them the nod. However, the 560's are no slouch in this area, too. They are both very addictive and hard to put down once you put them on.