Pros: Good overall sound quality, nice aesthetic design, one of the better "consumer" headphones you can buy at retail
Cons: Poor fit and durability, harsh sibilance
These were the first IEMs I bought that were over 50$ after reading good reviews on it. Unfortunately I don't think they live up to the hype. They are definitely better than some of the other consumer-oriented brands such as Beats, Bose, etc. but they are not worth 70 or 80$.
Note: I do not have my fully functioning S4 anymore because I recently lost it. (long story) The one I mention in this review comes in the blue CNET box (no cleaning tool, straight plug).
The sound quality is a V-shape signature with an emphasis on the highs. The bass is rather boomy but it does not overpower everything else and quite detailed still. The mids are a bit recessed when you first get these but they sound better after burn-in and using the bi-flanges clears them up while reducing sibilance. At first I found the highs to be rather metallic though this settled after burn-in, but the sibilance is still there. Overall, the highs are crisp but not very detailed. The soundstage is pretty good in size for an IEM. As these only go up to 19 kHz, they are a bit forgiving of lower bitrates. For my ears it is a bit harder to tell 128kbps from 320kbps compared to some other headphones. They also seem to amplify any sort of hiss.
Fit and comfort
This is probably one of the more disappointing aspects of the S4. Although I found the regular and large tips to be quite comfortable, the medium ones fall from my ears easily and moving them slightly off will kill the bass. Both cause the harsh sibilance I noted earlier. The "small" biflanges, on the other hand, take away this sibilance but take a while getting used to.They do take off a bit of detail from the highs unless you absolutely stuff them into your ears and keep it in that position (which I do not recommend because it has got stuck in my ear once). At the same time, they also bring out the mids and bass quite a bit more. Because the biflanges are small size, the noise isolation isn't as good as the large tips, although they still do isolate sound nicely. Like the medium eartips, they are hard to fit for optimum sound. Just moving them slightly off kills the bass.
Another problem is durability. The strain reliefs are especially weak and mine ripped within 3 weeks of use. That said, this isn't much of a problem as the cords still hold very well from the cans, and Klipsch has improved upon it in their latest version in addition to flatter cables. The cables in my version feel flimsy and do tangle when scrunched into your pocket, though they are springy so it's a bit easier to untie them. The straight plug on the other hand is poorly built. Putting these in my bag it somehow got bent to the extent that the center channel was removed like a karaoke. Fortunately, Klipsch sent me a free replacement (though I just recently lost this pair). It seems rather normal the plug is very slightly bent and not perfectly straight out of the box.
If they were under 40$ (which you may find on the internet) this would be a decent pair of cans. Unfortunately, durability and fit are the two main problems the S4 faces. That said, it's still one of the better consumer-level headphones you can easily buy at retail stores like Best Buy or RadioShack, stores that don't always sell the best type of headphones. if you are still interested, get the S4 II because of its better build quality (and watch out for the prices as it is often more expensive if they sell the original S4).