Pros: sound, price, size
Cons: shoddy craftsmanship
I really wish the RE0s lived up to their promise. They do sound really good, but they are clearly the product of cost-cutting. I bought a pair, and within a month, one of the buds was cutting out, and soon there after failed completely. I had them RMA'd, and within 6 months, the replacements began to fail (the adhesive that keeps the speaker part glued in to the casing is failing or has failed on both buds). I would have paid 50% more for these headphones and been happy if they stayed in one piece, but now, I wouldn't be happy if they had cost 50% of what I paid.
tl;dr great headphones crippled by terrible materials and quality control.