I debated 4 or 5 stars. But i really have no qualms with these at all. They check almost every box
PRESENTATION - Excellent. I believe they're pretty much the same as the M50x. Box feels very luxurious and high end and the headphones themselves are of excellent quality. Plastic but the subtle "clicks" when adjusting them and the clean style make these feel like a higher end product. I actually HATE the fact that the cups swivel so much. I get that they want to make them portable, but for me, these will never be portable. They're not big for an over-ear, but they are over ear, and the long cable makes it even more unlikely i'll be traveling much with these. But back to the swiveling - every single time i have to pick up and deal with these things, the earcups flop around and swivel like a dead animal. I always spend way too much time trying to "reset" them and get them back to the neutral position where i can simply put them on.
Cables are fine - it's nice that they included both coil and straight. I don't mind the length, for me it's fine since these pretty much stay at my computer, but some might prefer a shorter cable for mobile use. It is rather irritating that they chose to use both 2.5mm AND a proprietary locking cable. I would have preferred either simply a normal 2.5mm, or ideally a 3.5mm that can breakaway. But the cable quality seems to be excellent.
COMFORT - These are extremely comfortable to me. I edit video and i cant remember them ever really bothering me, even after long half day editing sessions. I guess some people advise changing the stock pads, but i have no issue with them.
I'd say that these are flat and neutral *enough*. For light video editing they are fine, but if you're a serious musician and need something for pinpoint accuracy when recording or mixing, these might not be it. For the price, they're probably as close as you're going to get (i think i paid like $75 for mine), but these seem to have a slight coloration to them, and i actually love it. Sound signature reminds me of my Vmoda XS, which is a huge compliment. They are fun and warm without being super inaccurate. They add some fun and punch to the music while still remaining true to it, and are excellent for bass heavy stuff, and do everything else well too.
BASS - Definitely seem to have emphasized midbass but they do subbass well too. Seem to me to have a slight V-shape and the mids are underemphasized to me.
MIDS - This is not to say that they are bad, because they sound just fine, but i listen to a lot of really loud, distorted guitar, and for rock/metal i prefer a more aggressive mid-centric headphone like maybe a grado or certainly my Sennheiser HD25-1 ii. Even metallica guitar seems a bit more warm and not as biting. Certainly not bad, but doesn't grab you by the balls like a good metal can should. They definitely do the job.
I wouldn't say that "laidback " is the best word to use, but it's definitely not the last word i'd use. They have a very non-fatiguing sound to me and remain engaging without any crazy harshness. I've never used these and thought that there was anything harsh about them.
Stuff like Radiohead's In Rainbows, and Beck's Sea Change sound very nice on these.
TREBLE - Something about the treble i really like. It sounds very "smooth" and crisp without being bright. The song Never Meant by American Football is an amazing song with some of the best drums i've heard and these 40x's deliver the attack and punch of the drums very nicely.
They don't sound incredibly detailed to me, but aren't really lacking to me. I do think at least a small amp is almost required. They're not insanely hard to drive and get loud enough off my phone (but not off my PC headphone jack), but definitely don't sound nearly as full, warm or detailed as with an amp. Even a small, cheap Fiio should be a requirement.
Guys, keep in mind through all this that i'm comparing these beasts against $200+ headphones that hit well above their weight class. For the $70 that i paid for them, they sound incredible.