Put it this way. I love love the HD650. Owned one twice. Expect to own another again in the future but promised myself I'd get an HD800 or HD800S first.
To me the LCD2 or at least the very one I'm listening to right now is much more dynamic - in the definition that quieter segments are quieter, louder passages are louder. The planar drivers on the LCD2, to my ears, have more resolution than what I ever heard on the HD650. But its odd, because its not as if the HD650 doesn't have detail, it just sounds a bit smeared - the 'veil' if you will. Although the LCD2 (and especially my version) is even more rolled off, it has alway had more fine detail even on the top end.
I'm sometimes at odds with the LCD2. Even in the past day, I'll listen to music on my D2000 and think "hey, I could almost just live with these" and toss around the idea of getting rid of my LCD2. But then, you sit down and really listen to a piece, something that is produced very well, and realize how awesome these still are.
Having one of those moments right now. I'm listening to a BT's new album right now, and he has impeccable production skills for electronic music. Listening to this album, it is so rich, spacious, and the bass - sometimes I think there isn't enough on the LCD2 - not so! it is perfect, especially with this album.
Not my most favourite music, but worth the experience.
Open in Youtube to watch in 4K if you have the resolution. For the impatient, bassier parts from 9minute on.