Pros: Good with all kinds of music. Very revealing of micro details.
Cons: Hard to think of any.
I bought these used in near mint condition and they were already burnt in.
The so called Sennheiser veil won't bother you that much. You might notice highs rolling slightly off on instruments like harps. Some headphones might make Loreena McKennitt's harp playing almost pinch your ears, but on HD650 it's a pleasure to listen to.
I have never owned headphones of this quality before and it was something of a revelation to hear FLAC files through these headphones. Suddenly I heard details and sounds never heard before even though I have owned some of my CD's for 23 years.
These headphones obviously needs a separate headphone amplifier whether you're going to use them on your portable rig or on your stereo. Ordinary portable mp3 players can't play the HD650's high enough and the headphone amps built into CD players and pre amps might not be of good enough quality to take fully advantage of the HD650's.