Pros: smooth sound reproduction, lush mids, slightly warm, impact and presence
Cons: forward mids can get a bit uncouth on some recordings
Please excuse my inexperience in reviewing audio gear - however I wish to contribute what I can to information on this product.
First a bit of background - I previously came from sony ex700, earsonics sm3, and HifiMan reZERO. es5 is my first custom, and the closest earphone I have heard to it is the earsonics SM3 which I will be using as the basis for comparison in many areas.
Starting with bass, the quality is quite good, impact is moderate and speed copes quite well also, but it is not as tight as bass on reZERO, but definitely more present. Others have described a midbass boost and I would have no trouble believing this. Extension seems adequate.
Midrange is the strong suite - it is smooth and slightly forward, as well as slightly warm and rounded in its note as described elsewhere. Female vocals are truly lush and sound amazing. Male voices are quite good, but the same lushness tends to soften them a little. The coherency of voices is excellent, but overall i prefer a little more edge with tenor voices to enhance the sense of vividness. However with some recordings the forward mids can get a little uncouth as per earsonics sm3.
Treble is detailed, and given my sources and hearing I cant comment on extension. What I can comment is that the timbre can seem a little dry at times. There isn't the same degree of "wow that cymbal sounds like its actually made of brass" that I got from the sm3 (its close though). Treble detail though is very good, as is speed. But I am being really picky here and many people don't seem to have a problem here.
The es5 has been described as smooth or rounded in its presentation of timbres, and this I find accurate. The edge and agression on some other earphones such as reZERO is toned down a little. This seems to reduce fatigue quite a bit. Overall impact, pace and presence is excellent which lends to really great PRAT. Instrument separation is excellent, it is really too easy to follow individual instruments or hand on a piano.
I find these very comfortable from first fit, which is really something for a custom. Isolation is excellent. As with any custom though, chewing feels uncomfortable and weird. Overall these are a very well rounded high grade custom with great comfort, and a very coherent sound reproduction that hides it's crossovers well. What I consider shortcomings in the sound reproduction may to others be strengths, or not issues at all.