What is it, exactly, that they do well?
And what do they do poorly?
I have had some for a few years and... I just don't get it. Their bass is capable, if muddy, the highs ate noticeably present, but slightly harsh, amped our not.
The sound signature isn't particularly clear, detailed or musical, but at the same time they're not thinking bass monsters...
So what exactly is it that people who love them love?
The M50s are neutral with a midbass hump and hyped up highs. They have a good amount of detail retrieval. They have almost no soundstage or imaging. They isolate very well and don't leak very much. They're stylish and sturdy. They're comfortable and easily driven out of nearly anything.
Most importantly though, they're under $150. For the features and qualities you get, at such a low price, they're amazing. The sound is good, but it isn't the best. But the M50 hits everything else spot-on.