First of all, I would like to say how informative this forum has been. Since I joined, I have purchased the Sennheiser HD438 and Brainwavz M1 as well as a FiiO E5 amp.
I've had the HD438s for 2 months now, and I feel like I'm ready to give these a noobie's review. I don't really have other headphones to compare to so I will compare them to my Brainwavz M1 and my Creative EP-830.
Eh. I don't feel that these headphones are particularly well built. The plastic is typical Sennheiser plastic, and doesn't feel quite as solid as I'd like them to be. One ear cup has more resistance in swiveling that the other one.
These headphones are amazingly comfortable. Period. Very low clamping force, yet stays on your head very well. I bring them to class and they don't move around when I walk. I am a glasses wearer and they are still pretty comfortable.
These are closed circumaural headphones and do isolate sound somewhat. However, I can still hear a lot of the cars out on a busy street and I can't wear these in the library because they leak quite a bit of sound.
Here's really the meat and potatoes of this review. Although I am a new audiophile, I have been a piano player for 10 years and I am quite picky with audio.
Overall, these headphones sound quite hollow and cold, which may not may not be a bad thing. The bass is NOT as advertised and is not very powerful at all compared to the brainwavz. It sound really hollow and overpowered by the mids an the highs. FYI, I am not a bass head, but would like to have the base appropriately depicted. The mids on these headphones are exceptional, brightening up vocals quite a bit as well as a very accurate depiction various instruments. I found the highs much too forward on these phones, often too sharp for me to listen to without fatiguing. Another problem with this headphone is that it gets really messy with tracks with a lot of instrumentation and can sometimes drown out vocals.
The sound stage is pretty small in my opinion, even compared to my Brainwavz M1, although they are better than my EP-830.
I am no audiophile by any means, and I hope that someone finds this helpful. =)