Before getting my M80's I read a lot of people talk about what revealing speakers they are. That they shine with good recordings, and show the flaws of bad one's. I fully expected at least half of my music collection to be unlistenable on them as I had heard there are plenty of CD's that are/were recorded very poorly.
Much to my delight however I have never played a song and immediatelly decided it must have been recorded by a bunch of idiots. Every song I've played to date (including MP3's) have sounded just as astonishing as the next. I will admit to hearing rather brilliantly recorded music. But the songs that haven't been 'extra special' haven't puked themselves out of my speakers... They just weren't, 'extra special'.
So all in all I have to say, I haven't been disappointed by anything.