My initial experience with the ESR was that of buyer's regret. It sounded a bit too flat for my liking and had a weird mid bass lift.
After a few days and once I've adjusted to the signature, the ESR has incredible separation and clarity with a nice extended treble. The bass is tight and punchy enough, the mids are centred, without an obvious veil, and treble is extended but not too splashy. It also images very well with what I feel to be quite a good soundstage.
There isn't much coloration of music by this iem. It doesn't present songs with an increased amount of bass or treble and vocals are as natural as can be. It has a very neutral tone. Some would find this iem to be soul-less or unexciting. But to me it is doing what it's supposed to be: an objective iem that tries to be as unbiased as it can be. I've grown to be appreciate the sound and in turn, able to enjoy it
P.s. I'm someone who appreciates treble quite a bit, so take that into consideration. Also I can hardly tell a difference between 24bit and 16bit flac and v0 320kbps MP3, so I don't have the sharpest ears lol.