The reason that I worded it as I did is because (true, not all), but a few of the loudest hd595 supporters simply haven't heard that much to really judge. Not that I'm a walking encyclopedia of headphones myself, but it just wasn't hard for me to find something better.
On the flip side of that coin, I think these were made to be good headphones that weren't supposed to need thousands worth of source and amp to sound good, and tried to fill a gap of "go to the store, get a decent set of cans, and forget about it." To my ears, they just didn't get there.
As for my source, of course I'm a believer in synergy, but my source and amp really should be up to the task of the hd595, especially if they handle the hd650's with seemingly no problems (although I realize the hd650 scales up way past what I have in my sig).
I will say though, love or hate, give the hd595's time, one way or the other, burn in does have an effect, and even though I ultimately feel there's better, you have to take your time to get to the optimum hd595 sound.
My husband, who comes from the dt990 600ohm old old skool model that you can't even find a google image of anymore, made the comment when having a listen that the hd595s made everything sound like synths. He always tells it like it is, since headphones bore him, and I had to agree. He hit the nail on the head.
So that's two of us, but we live in the same house.