Pros - Lightweight, Easy Fit, Comfortable, Good Isolation, Decent sound for price.
Cons - Houses are cheap feeling (maybe that's why they are lightweight.), Cable, Sound sounds largely unnatural
I gave these headphones to my father some time ago. They were decent, but I have moved onto much better ones and have found my niche to be over-ears rather than in-ears, partly due to full-sized have better, real life sound, and also due to the fact that I had a major ear infection in my right ear a while back, and I believe it actually blew my eardrum. Now, there is almost always fluid buildup in my right ear, and my sinus issues don't help matters. In ear headphones simply perpetuate the problem, especially in ears that are meant to go deep into the ear. I am mentioning this because, simply put, the S4's were the worst in-ears for bringing about that issue with my right ear. I hearing is still good thankfully. During the time when I got the S4's, I got them as gift. This gift was actually a pair of S3's. With rockbox on my Sansa, I blew both S3's drivers in a matter of ten minutes, and the ten minutes before destroying the drivers, the sound was horrible. The S4's were a godsend compared to the S3's. Like the S3's, I liked how lightweight and comfortable the S4's were. They went deep in the ear canals, but did not seem like they were. Isolation was as good as many headphones are with Comply foams.
The sound of the S4's is great really, and they certainly deserved the praise they received. I loved the bass that came out of them. Unlike other in-ears I had before, namely the Skullcandy Smokin' Buds, they bass did not cause eventual loose drivers and the annoying rattling that came with it. The S4's were really my true step up from crap that came with the Sansa and the not much better Skullcandy's. I of course knew that those headphones sounded terrible, but I wasn't well versed in the world of headphones at the time. The mids and highs were decent, although did not stand out. I can't say they were dead either, but the S4's clearly focused on what many and that range, and even more expensive headphones do: Bass. The S4's bass cannot be compared to the terribly overprices Beat's bass, but the bass is actually clearer and more natural sounding than the Beats. The mids and highs are clearer though. I know I am comparing in-ears to over/on ears, but it seems that headphones like the Beats are what everyone compares another headphone's bass level to. Overall, what I did not enjoy about the S4's was the overall unnatural sound. This is caused by a completely non-existent soundstage, and that magical resonance after an orchestra ends or the depth of the drums being behind the singer are not there. The orchestral notes simply become quieter, rather than echo away, and the vocals and drums sound next to each other and right up in your face. Don't get me wrong, the S4's sound good, but they sound like in-ears, while there are some in-ears that manage to actually sound like over-ears. When I was into in-ears, I never bought them because I like the sound of in-ears over over-ears, I bought them for portability, but sought a sound similar to the over-ear size. The S4's don't live up.
What really hurts the S4's I find is build quality. First, the driver housings seem to be made from a thin, easily cracked plastic. I never had anything happen to the housings, but was always thinking about something happening. The S4's cable is terribly thin and tangled. Just before I gave the headphones to my father, I noticed wear in some of the sheath, and it was going a gray color, versus the original white color. The area of the sheath felt pelt-like, or powdery. It never wore down to expose the cable, but I doubt there is much left until it does. Lastly, the cable doesn't fit tightly into the rubber stress relief rubber on the base of the housings, and that lead to me thinking a slight pull will put the wires out of the driver. To make matters worse, the rubber parts have molding seams and of bother housings, the rubber split on the seams, essentially making the stress relief non-existent.
Overall, the S4's are decent, offering good sound quality for the price, but they fall in quality. For $80, I think it is hard finding better sound, but for a bit more, you can get a pair of Shure SE215's, which don't sound similar to the S4's in any way really, but their sound impressed my about the same amount. The SE215 are top notch quality though, and maybe the few more dollars for them is worth it.