Talk genres. Also, comparison to HD650 and HD800?
I'd say they're pretty much an all-rounder in terms of genres, but it does better with EDM and more bassy stuff like hiphop. Classic rock still sounds very good on it. I really enjoy Hotel california by the Eagles, Money by Pink floyd and Brothers in Arms by Dire Straits on them, for example.
I'm not a fan of the HD650, so this might be a bit biased towards the N90Q. It's also been over half a year since I heard the HD650, as I sold it quite a while ago. From memory, the HD650 sounded much more muddy to me. The N90Q has better textured and stronger bass, with a tight punch. The N90Q also extends much better into the sub bass. From memory, the soundstage is pretty identical, although the N90Q seems to have slightly better instrument placement. The N90Q does have much better seperation. I don't feel confident enough to fully comment on the mids, as I can't remember the HD650 mids as well. The highs on the N90Q, while not as good as most summit-fi cans, are better than the HD650s highs. I found the highs on the HD650 very lacking. The N90Q can sound slightly 'shrill' at times, but that's mostly with poor recordings. To completely hear with I mean, try the song 'Eminem - Legacy'. Youtube will suffice. Try the song with a n audiophile grade headphone. Whenever the female singer breathes in, or pronounces the 's', it sounds very shrill and peaky.
Onto the HD800.. The HD800 and N90Q are a complete different beast. Overall, I would pick the HD800 over the N90Q in terms of Sound Quality. But remember, the N90Q is a stylish ANC portable headphone. This is why I have both. The soundstage on the HD800 is much better than the N90Q, so is the instrument seperation. The bass punch is much better on the N90Q. They both extend very well, but I feel like the N90Q bass texture is more present. The mids and highs on the N90Q sound very forgiving, compared to the HD800.
The N90Q makes music much more enjoyable than the HD800, but the HD800 will let you hear every micro detail. That doesn't mean the detail on the N90Q is bad, by any means.
For home use, I would recommend the HD800 over the N90Q anyday. For portable use though, the N90Q might be the best offering on the market (unless you think the Sony R10 is portable..).
I hope this clarifies everything a bit, if I missed something, please tell me. As you can probably tell, I'm having quite a hard time describing the N90Q. It's such an unique beast, and the placement on the head is very important due to the Trunote technology, and with all the extra options (standard/studio/surround and bass/treble EQ) it's hard to truely give impressions. I would strongly advise you to demo it before buying, as this is not your typical headphone. Or atleast have a possible return period when you buy it. This headphone has a somewhat consumer-ish sound, but with an audiophile twist.