Pros: Amazing isolation, Transparent sounding, Extremely accurate, High degree of imaging in mid and treble
Cons: Bass is uninspiring, Product out of the box is a poor representation of the device -- burn in absolutely required.
First off let me preface by stating that I bought these on a whim. I had read many things about Etymotic's penchant for accurate reproduction.
The initial impressions I got from these were a mixed bag. First off, I love the isolation factor, putting these on in the middle of a crowded communal area was like stepping into a library. I tried the various silicone pieces which were provided as well as the obnoxious chunks of foam and settled back on the medium sized triple flange which was installed on the unit from the factory. These tend to sit a little further inside the ear canal, however once they are in I didn't find them to be any more uncomfortable than any other IEM I have used, after a couple of hours it's like they don't exist.
Sound quality out of the box was disappointing. There was a slight hint of bass which seemed to lack much in the way of clarity or substance. Through the mid and upper ends of the spectrum were just simply "there" along with some harshness and a hint of sibilance. At one point I wondered if these Etys were defective in some manner, I have read many dozens of reviews and generally Etymotic products are considered to be highly accurate. Out of the box, I listened for around 30 minutes before packing them up until after burn-in.
Burn-in was accomplished over four 24 hour periods, one period each for white, pink and brown noise and the final period being a random selection from my music library. Sound level was consistent for each test, being set at 0.5db above what I felt was a "loud" listening level.
Following the burn in, I wedged them back into my head and went for another listen, and things were very different this time around. The bass had been cleaned up significantly, and while there wasn't a tremendous amount of it in any regard, that which was there was extremely accurate. Through the mid-range and high end things were very sharp, crisp and present. The hint of sibilance which I had detected before break in was gone, as was the harshness. Imaging had also managed to improve by several orders of magnitude. Listening to any sort of symphony, orchestra or choir through these devices was truly a treat, you can almost feel the vibrations off the strings. At some point, I stopped thinking about the devices themselves and simply enjoyed the music.
In terms of overall listening experience, I rate them above average for all but the lower frequencies. I feel that they could have done with more presence to compliment the accuracy. I would also like to point out that the middle and high frequencies were amazingly revealing of the source. In my listening, compression artifacts were readily apparent for 128k and 256k mp3. Artifacts were less present in 320k mp3, however they were still there at various points if one listened closely. As anticipated, lossless encoding formats presented a truly clear aural picture of what the music was intended to sound like.
By the time I pulled them from my ears almost twelve hours after picking them up, I can definitely say that I now know where Etymotic's reputation comes from. The device which I pulled out of the packaging was not the finished product by any means, however the device that I retrieved from burn-in was the most accurate listening device I have ever had the opportunity to own.
Looking at all of the factors, I would recommend these to anyone who prefers the mids and highs to be very strong, present and almost close enough to touch.
That said, I would not recommend them to anyone who enjoys a lot of bass with their music, these will almost certainly fail to deliver the volume, bass presence and impact of many other devices available.