I finally received my HD650s after a long period of wanting to try them and my first impression was similar to what people have been saying. There is nothing on these cans that blow you away, but everything sounds.... right. After taking them off all I can think about is when can I put them back on? It's weird, but in a good way. I love the way the HD650s make, and pardon the corny description, a soundscape bubble around my head. Like there is this large bubble and the music just completely fills this space around my head.
Of course, I also noticed something odd when testing these headphones. It seems that when using the HD650s with my Matrix M-stage amp, I can hear the infamous veil that some people talk about. It's almost like I put a piece of cloth in between the headphones and my ears. It's there because when I hook the HD650s directly to my Auzentech Forte soundcard the sound is crystal clear. I mean, it is really really nice. It completely removes that veil. The treble is nice and detailed. The bass is there in full force and of course the famous mids are probably the best I've ever heard from a set of cans.
It is a little disappointing to see that my m-stage won't cut it with these cans, but I am nothing but happy about my decision to buy the HD650s.
See how you get on with them for a few months and then you can always try the foam mod. I'm one of a few that really hears the benefits. I only have the foam removed from the driver, not the inner ear cups. Again you will need a good amp to make sense of all the extra openess. The detail and dynamics are much more, but it is the bass that comes out the most... for better or worse there is much more of it.