Haven't tried the M50 before, but I do own my 6 years old ESW9 that's very actively used. Build issue can be a problem though it's made in Japan.
Sound wise, think of it as wearing a tube amp on your head. Sounds warm, probably due to the wood enclosure. Forward mids with luscious vocals. Especially female vocals. Bass impact is there, but not bloated. Which I like. Highs are a little rolled off though specs say 35kHz. Never trust specs, haha.
Not really suitable for fast paced music, more suited for jazz and whatever similar in speed. Comfort is above average for something supra-aural thanks to genuine lambskin ear pads. Isolation is horrible though, and better suited for home use. Wood enclosure is hard to maintain too, easily scuffed. But no denying it's visual sexiness.
Added: soundstaging and detailing probably not the best, but that's (average details) what makes it easy on the ears and intimate. I will never be selling mine because as coloured as it is, it sounds so damn fantastic with the right kind of music.
Edited by alleggerita - 5/22/14 at 1:59am