Most of my impression are gonna be based and compared against the SE535 as it was the only pair which I had spent long enough time to be able to make a proper comparison.
Sound stage: In terms of sound stage it definitely improved. Makes live performance more enjoyable.
Highs: Its definitely an improvement from the SE535. However I actually hoped for much better performance considering it now a quad driver.
Mids: As usual the smooth mids that Shure has as always had. Rather similar to the SE535. Something that has kept me a Shure fan till now. Being a vocalist myself, I really love to listen to the vocals a lot.
Bass: Definitely more bass and tighter too however if you are a great fan of the JH16 and love it for its bass, the SE846's bass is not gonna come close IMO.
All in all it a better version of the SE535 and in terms of overall performance its 1.5x of the SE535. Whether or not it justify its price tag depends on you.
Hopefully it may improve after much burn in. Its my first impression and base on my own opinions. Feel free to share too
Cheers