I have the HE-500, and I'm starting to feel the same way.
Yes, the HE-500 is awesome, but is it $699 awesome? I'm not 100% impressed to say it is. I guarantee something is around or will come along in the $300 range that will eventually match or exceed it.
The Piston is a great example. It craps all over much more expensive iems and is very enjoyable, for $20.