I contemplated for about a year whether I should try them, wondering if they would deliver a worthy upgrade over the classic DT 770 (considering the higher price) - Luckily they do!
I never found the DT 770 pleasant for listening, but I like their detail when producing. I am pleased that the HD 490 not only excels in both scenarios, it is also vastly superior. It ought to be given the higher price, but you never know. They do not feel as durable, but on the other hand they are lighter.
The HD 490 sounds very natural. Detailed but pleasant. Gone is the odd 4k dip and harsh high end. The stereo field is wider and the low end more precise / less muddy. In my opinion DT 770 is not good for mixing, but the HD 490 is. They cannot replace a set of good speakers (never tried headphones that could), but they do an excellent job.
One slight concern is that the headband cannot be extended very far. If you have a big head, voluminous hair or wear a cap, they might not extend far enough to fit over your ears. These are the first headphones I have ever owned where I have to extend to the maximum possible position.
Tested with a MOTU M6 interface.