Pros: Balance, transparency, treble extension, detail, speed
Cons: Bass quantity, cable quality (cloth version)
Housings are made of metal and are solid but the cloth version of the cable is prone to microphonics. The jack is fairly weak and the strain reliefs aren't particularly effective. Fit is easy as the earpieces are fairly small and isolation is just above average.
Sound is excellent for the money. Treble is more prominent than in most earphones but is never harsh and has better extension than anything I've heard, detail is excellent. The midrange is natural sounding with little colouration and is also very detailed. The RE-0 is light on the bass but extends fairly low with excellent speed and punch but little weight behind it.
Amplification helps improve the bass quantity, punch and speed some more and overall dynamics are improved. They sound a little sterile without an amp but do not need one, they just scale well with the added power.
Overall sound is airy and slightly warm and suitable for a wide variety of genres but not anything bass heavy. They are very revealing and detailed but not agressive with the detail and are quite relaxed sounding. Transparency is excellent and the individual characteristics of the recording really shows.