Pros: clarity, comfort
Cons: mid bass response
"They may disappoint bass-heads, but for anyone who strives for true audio reproduction, this is the IEM for you. "
I'm not a bass head, but I don't hear true audio reproduction.
Yes the bass response goes down low, evident in a song like Nick Cave Red Right Hand, where the almost sub-bass frequencies (<50Hz) are clear. But I do perceive a slight dip around 50-100Hz. So in an acoustic track the double bass can be hard to hear, in a rock track the kick drum lacks punch, the bass guitar lacks depth. It's only slight, the rest of the spectrum sounds beautiful, but the EQ down low does not sound flat to me. That's out of the box tested on iPod nano first gen, iPod 5th gen, ipod 4th gen and iPhone 4s.
Added note: I've started using these with the rubber tips from my Ultimate Ears and it improves the bass response slightly. I think the rubber tips on the RE0s are too hard and it's hard to get a good airtight seal.