A quick sidenote I actually own the ATH-A500 headphones but they use the same drivers so the review should be similar.  I picked these up on a whim at this place that imports Japanese products for around $100.  This is my first pair of SQ headphones so I was suprised to find how big they are, the drivers completely cover your ear.  My favorite part about these things is how comfortable they are, I could seriously wear these all day and not have an issue.  For the price these things sound incredible after break-in, the bass is clean and deep and the highs are just right.  Being closed headphones they don't leak out much of any sound out and that's something I really enjoy as well.  Lastly, these things really open up when you amp them, I saw much improved bass and mids when I got my Headroom Total Airhead hooked up to them.
 
That being said a few gripes I have about them, the build quality isn't the greatest, at times I feel I might break the top part.  They are not something I would get for portable listening.  The only actual issue I have had with them is the foam earpads wore out after a few years, which isn't that huge of a deal since you can contact Audio Technica for replacements for around $12.  I guess the sound quality might not be up to par for serious audiophiles, but then again why would they want to spend only $100 on a set of full sized cans anyways?