Pros: Very comfortable, easy-to-use, consumer sound
Cons: Tends towards sibilance, better options for the price
I bought these alongside the UE500, with the intent of keeping the one I liked and returning the other one. Auditioning through a stereo, the S4s were a little less lively and smooth than the UEs, and tended towards some fairly bad sibilance, especially on classical tracks with high violin parts that were almost painful to listen to. I liked the UEs better, and returned these.
Despite the sound quality issues, I have to say they were very comfortable and hassle-free, and the build seemed better than the UEs (which have had cable issues since).
Keep in mind that this was a while back, before I had a lot of audio experience (still don't), and that neither pair was burned in.