I have had my HD598 for over a year and what I could say about this good looking, gorgeous headphone is it is very very smooth, silky smooth with nice enough details for 80% of my taste. The bass is the weak point of this headphone, it is not too strong not too weak but just enough for most of genres. The sound-stage is big and accurate, separations among instruments are good, I think sound-stage is better than HD600 and HD650 that I tried. The midrange is not as good as I expected, because the smooth signature so It usually fits slow, light vocals such as Jazz or low voice singers such as Susan Wong, Emi Fujita, .... if you look for aggressive, high note, powerful vocals you should look for other headphones. Besides, this headphone is absolutely good for movies and games with the sound-stage you can imagine that almost everything in movies and games is really amazing, lively such as you are living in them.
Recommend these headphones for Jazz, slow vocals, easy listening, instruments, games, movies. Not great for powerful genres such as Rock, singers such as Toni Braxon, Whitney Houston, Maria Carry, Celine Dion, ....
My next headphone could be LCD-2.2 but It would take me for 1-2 years to save up enough money to build LCD-2.2 combo (with DAC/AMP).
Happy to share my thoughts and considering upgrading the better cable for this headphone.