The M50s seem to be fully burnt-in when I tried it again last night (though I'm still running it through white noise, pink noise, etc. right now...) and I find it really good. As in it seemed like a Eureka moment when I finally heard the treble more clearly and the bass bloat was gone.
Definitely a different sound from what I'm used to but I think they will make a great all-around headphones when I'm not looking for a specific sound. It can't beat the Etys for any occasion when I just want transparency and detail. It can't beat the Grados for that rousing in-front-of-the-band effect. But I find it very balanced and so far it's done a great job with different kinds of music. I also found it excellent for watching video (on the Mac) and I'm thinking I'll probably use it for some gaming if I ever get back into desktop games. I haven't tried it with console games or watching movies on the big TV, and I'm curious how that will work out (I used to have a pair of old Sony stuido headphones in my Playstation 1 days and that worked out pretty well).
So I will probably keep them for now until I find something better. :)
To the OP -- enjoy your M50. But I highly recommend a burn-in period and using it with an amp whenever possible (although they're great un-amped, too). :)
You are correct, Sir.
As has been discussed many times on these threads 25 - 50 hours of burn in and they become incredibly good. The bass tightens up, the strident highs subside and much of the recessed mids seem to emerge. It's a wonderful thing and I am extremely fond of these HP's. I also happen to find them very comfortable.
I don't think they are very balanced, but close enough. I just like the sound they produce.