I absolutely love my HD650 and still looking for a worthy replacement. They just sound "right" to my ears. More importantly though, they sound consistently good across all genres of music I've tried. My Hifiman HE400i sounds better with only selection of music, but the HD650 sounds almost as good with the same music and way better for everything else.
If there is one defining characteristic of the HD650, it would be the mids which sound in another league to my HE400i. They add this lush, meaty and palpable quality to the sound that no other headphone I've heard can properly reproduce. Even the treble sounds 'thicker' which doesn't really make sense, yet it's one of the first things you notice when you compare them. My HE400i whilst having clear and upfront mids with better bass extension, just sound thin in comparison. I can go into more detail as to why this is, but as I said before the HD650 just sound "right" to my ears, whilst the HE400i are "not quite right". This is most obvious when you listen to vocals, which sound scarily real and up close with the HD650 but a little distant and synthesized with the HE400i.
Regarding the Sennheiser veil, I think there is a veil, but only because other headphones are too bright. Whislt I think the HD650 could do with some more treble extension, I don't think they need more in terms of quantity. I also think it's a positive to have slightly relaxed treble response as you rarely get any of the painful sibliance or general harshness you find with many of the other audiophile headphones. It's better for your ears too as I've listened to the HD650 for hours on end at seemingly high volume without any fatigue at all.
The last point also leads on to another great thing about the HD650 which is their exceptional comfort. Sure, they might not look that fancy and don't make use of any exotic materials, but its well built and perfectly functional. Soon after I put them on, they just disappear and I feel like music is being sent directly into my ears from thin air.
I'm actually considering buying a new pair of HD650 just to keep it as spare, they are just that good.