Pros: Decent "punch" for certain music/awesome DJ set/VERY COMFY
Cons: Muffled sound/ not very "musical"
First things first...I was expecting WAY better sound than this after having read over 30 reviews from all over on these phones....I would say the "warm" sound people speak of is the most prominent "feature" the M50's have.
Taking the M50's off and then putting on my Shure 440's made is seem like a curtain was lifted off of the music and can finally clearly hear the details the music has to offer. I find myself searching and looking for details while I wear the M50's, and can simply listen and hear all the music when I wear the 440's. Using bass testing FLAC files on my Xonar sound card (192k/24bit & amped), the M50's do have some nice qualities in the mid-lowish bass range and the amount of bass is decent too. I suspect the thick padding on the inside of phones to comfort the ear could be a culprit to some of the muffled qualities.
Games movies with the M50's carried with it these same "muffled" qualities, like people are eating bread while performing their music 
.
I play SC2 and Mass Effect 2, mostly. Sounds such as opening doors, background voices, weapon sound details, etc didn't sound nearly as clear as the 440's did. With the 440's I feel like I'm in the spaceship and fully immersed in the action because all the details are clearly heard. The M50's give me no such feelings, mostly meh. Sort of like watching a play from the upper comfy expensive seats in theaters that are quiet enough to have a conversation. To be fair, some the bass and some of the mids do sound quite nice and mostly with effects that have punch or rumble.
Overall, I find them an okay can at best. They'll be a great replacement for someone who has $100-$180 to spend and enjoys terms like "punchy bass" and "warm sound" maybe somewhat "neutral".
I had actually bought these because I thought they were going to be replacing the 440's but.....NOT. A. CHANCE. I basically never use the M50's, even after 15+hrs working them in. If I was a DJ, I'd likely keep these but will be selling them instead of becoming one.
Wearing them on my head is another story. It's like I have a playboy bunny hugging each of my ears while another is draped over my head. Mmmmmm. Mark these up @ 6/5 stars for comfort. Keep this in mind, travelers, they are also comparatively light.
The 440's let you hear everything very clearly throughout the entire frequency. The bass is very detailed, but there isn't quite as much as the M50's. Sometimes, with the 440's, the highs do get tiring with music at higher listening volumes because Shure probably put more juice into the higher frequencies, anybody know 4 Shure? This is most present with music that involves alot of cymbals, or alot other very high-pitched sounds. So super hard rock and metal might not be ideal for the 440's & better suited to the M50's. Also the quality of the recording would be more important to the 440's because of their detail.
I tried the Shure 840's at a store and quite liked those as well, they sound just a little better than the 440's. Price was a little high though.
I am by no means a pro audiophile, I just have a naturally discerning ear & I'm very picky and critical of stuff I buy. I thought I'd share my 10 cents (inflation has risen since the 2cents days.)
Thank you for reading, head-fi's.
edit: After 80+hrs burn in, nothing new to note for M50. Although the 440's continue to tickle the area below my stomach. Looking forward to changing the ear pads.
Also, why do you people evaluate stuff on a computer audio cards that have no amplifier of any sort? I have M-Audio 1010Lt card, a professional audio dedicated card, and it makes almost all of the headphones sound differently from how they sound through an amplifier. It just sucks the power out of them and shrinks the bass response considerably, even on such power efficient models as ATH-M50 and HD595.
You're commenting in the wrong place when you speak of proper mixing and sound reproduction, you're in a m50/440 thread, you need to hit the $500+ mark before you get anything you can call close to really good. I can get a similar sound to an m50 by putting my shirt over my head, then the Shure over my padded ears, it's quite interesting.
What you need is an lcd-2...it's what the pro's like to buy here for proper mix judging and creation, this sub $400 stuff doesn't cut it and gets sent back. I'm pretty sure I was just pooping on m50's $/perf., & not putting in $150 worth of phone in their phones. I don't say the 440's are the all in one cure for cancer.
Ok, I see now that with this attitude we're not getting anywhere :)
It's never about the price of the equipment, it's always about how it sounds. Now I haven't heard the LCD-2, and I cannot say if it's better or worse than M50. It doesn't make it better just because it's 5x as expensive, that's for sure. In my book, it might be worse (if it's hyped like the Shures are) or indeed it might be better. All I know is, from my experience, M50 is a better headphone for audio production than SRH840 is.
Not hearing entire parts of recordings (M50's), at least in my book, does not mean "balanced sound". Most of the background stuff (including instruments) in Pink Floyd music is almost inaudible unless turned up higher than wanted. Rush looses all their presence & Dream Theater is only good on the M50's when Portnoy is laying in on the kicks and you can hear the bassy thump. Dave Matthews sounds like he's got the microphone cover in his mouth. This may be a wanted feature for some cavemen recorders but in this world, most people like to hear everything clearly.
See, I know this because I've talked to and watched hundreds of people come in and out of the store. No one ever comes in wanting to hear more sound less clearly. This just shows how far people will go to defend their babies. Shure is not "my brand". Shure only got me nearly $200 bucks worth of sound in a $90 can, clear sound. My M50's left me wanting more, so much more, especially after all the rave reviews (including yours) I had read. I expected the M50's were going to blow the 440's out of the water. Had I known how bad they were for what I paid, I would have saved up just a little more and gotten some DT770's or 225i's. At least I know now, through my experience with rayj and flower boy what "qualites" to look for in online fanboyery. My boss is a fanboy, loves his M50's, but hates all 6 of them sitting in the back, waiting to be sold..duh..same thing as last year...and the year before. Look bud, I know you love them like a child, but I think enough is enough. They are not a good phone @ their price range. Just mediocre at best. Like Dre Beats, you pay for name first, flash second, and quality last.
I could never understand this kind of logic: if people buy it, then it's good, so I'm not really following your point here, I'm afraid ;)