I am really happy with the sound quality of the RE Zero.  The bass is much improved over the RE 0, but still maintains the clarity and distortion- free quality that the RE 0 has.  Everything else about the sound quality is the same if not better.  The build quality is very solid, and the gunmetal finish is very good looking.  These headphones are great for a variety of genres, and I listen to everything from Alternative to Classical music.  Meany headphones have trouble portraying the complexity of large scale orchestral pieces, but the RE- Zeros handle everything just fine.  The 16 ohm impedance allows for easy use with portable players like i-pods, and I see no need for a portable amp when you are on the go.  The adapter that everyone complains about is actually smaller than I thought, and is not a problem for me at all.   Lastly, you cant beat the value, for an IEM that is consistently being compared to $300 IEMs, the fact that they can be purchased for less than $100 is unbelievable.