If you are looking for a closed headphone (will block out some ambient noise) these cans sound great. I personal prefer open cans.
but wanted to try something that would have more bass response, and let me tell you when they say they go down to 5hz
yes 5... it will shake your brain. i went with the 80 ohm and am running with a headphone amp. i did try off my mobo audio(PC) and my home receiver all sounded good.
If your planning on running off your cell phone they sound good, but not going to push them like they need.. And the cable, non detachable and long, but good quality.
There are some modes people do to these to fix some inherent problems. Adding sound dampening to the back of the ear cup, to deaden the reverberation, noticeable if you stop music at high volume.
Soldering in a female 3.5 jack, to make the cable detachable. all these things need to be done to make these more consumer friendly.

In there defense these are for studio monitoring, not portable usage. And they are great for critical listening, or just enjoining some good music.

Oh, My, Goodness........When I first got these I was disappointed because my phone and my laptop could not drive these very loud. I had an SMSL tube amp and it still could not push these. It also had a slight popping sound that I originally thought was the headphones but turned out to be the 3.5mm headphone cord from the computer to the amp. After I got that fixed up, I had already ordered an 80 ohm version to replace the 250 as well as an FX Audio tube preamp. I compared the 80 ohm and the 250 ohm side to side using 3 different sources (turntable, phone, computer). The 80 ohm just cannot compare to the 250 ohm version. The 250 ohm version does have some very bright highs, and subdued lows compared to the 80 ohm, but the lows are much much more precise and punchier than the 80 ohms. The brightness is rounded off quite a bit when run through the preamp and amp. The 250 ohm just simply put reproduced the sound to a far better extent than the 80 ohm. The 80 ohm version is great, don't get me wrong, but the sound from the 250 ohm pair is just not comparable to any headphones I have ever heard, simple as that.
You really, really, really....did I say really? Really need a powerful amp for these. Even my SMSL alone was not enough to power these to any sort of high volume. The preamp increased the gain and made these useable with the SMSL and even "tubed" up the sound a bit more! I just cannot say enough good things about the 250 ohm version. They beat the hell out of anything else at the $150 price point.

I bought these and a few other pairs that I tried out for a few days before settling on this set. I went with the 80 ohm version and this is plenty loud when driven by either my laptop or desktop. The sound quality is very clear. One note I will say is that the bass is not very high on these headphones. After getting used to this I actually prefer the sound, but if you are coming from beats or similar they will noticeably sound odd for bass heavy songs. This can always be fixed through software though if you decide you really want more bass. The main reason that I decided to keep this set was comfort. The ear cups are huge and this works excellently since I wear glasses. Other headphones I found would push on the ear peace of my glasses toward the back of my head. This set easily encompasses my entire ear though and does not have any single pressure points. It also isn't a large amount of pressure on the temple piece of my glasses. I did cut a Nerf dart in half and put it in the headband based on another comment. It was a really easy process since the headband has snaps to easily take it on and off. I found without the dart the headband would start to hurt after wearing them for more than a few hours at a time. With the dart I barely notice the headband.

First pair of higher-end headphones and was blown away at the sound difference. If you have glass, I cannot stress enough that this is the best you will find. Any of Beyerdynamic's velour pads will suit you better than any other headphones. I wear them for HOURS and they do not hurt my ears (as they go over, to my surprise quite comfortably) and they are fine putting minimal pressure on the glasses arms. I used to get really deep marks from my glasses arms for using rough headphones, not much anymore.

SOUND: Amazing sound, bass and presence (over 5k) are hyped a little, but not too much.
COMFORT: One of the best cushions I've tried for a headphone. It might be a bit tight if you have a large head, but you'll get used to it.
DURABILITY: Feels pretty strong till now (2 weeks). I'll update this after a few months.
VOLUME LEVEL: 80 ohms is enough to get a loud sound on laptops. On the phone I usually keep the volume 90-100% for a good level.

Regarding the big question "can these be used for mixing"?
I know these headphones are not meant for mixing, but I still mix Electronic Music seamlessly with these. Its great for hearing the sub range and low end which is difficult to do in flat response headphones. I would suggest you have something like a AKG K240 along with these just to get a more realistic sound.

Another big question going around: "Is it better than the m50x"?
Both have their pros and cons.
m50x is more closer to a flat response, definitely more portable and ships with 3 cables interchangeable cables.
770 are better listening headphones. Around the ear cups mean better 3D sound, better build but heavy and less portable.

I was confused for a long time but decided to go for this when I saw it on sale at 124$ (less than m50x for the first time).