I prefer open phones as I often listen for a long time and get hot ears. I discovered the HD238s at my local Apple store, and promptly bought a pair (that night, from amazon of course) as they sounded virtually indistinguishable from the much dearer Bose phones they usually have on display. I was sure they'd out do my PX100s.
Having had them several months now, I don't expect to be using them much. IMHO, they're ok at medium volume, but sound a little muffled and emphasise the bass too much at that sound level for my liking. They are intended for portables, and the Amazon description says they are "Optimised for iPod, iPhone, MP3 and CD playerss". I'd guess this means they empahise certain frequencies to somehow accenuate the experince of listening to compressed music on the move, like in a semi-noisey environments. Just a guess, I know, but the description must mean something.
Again, in the Apple store they sounded great - and they still do if I ever feel like blowing the cobwebs out of my head. But they also (still) seem to distort high frequencies occasionally (most irritating) and when I'm listening quietly to FLACs or CDs at home after a short while I start rummaging for my old PX100s or my daughter's Koss Porta Pros as they don't sound detailed enough to me. Both these much cheaper phones seem to sound clearer to me. Which leaves me still looking for a low/mid-range priced phone.
For anyone who already owns the PX100s, or similar but cheaper Koss Porta Pros, I'd recommend skipping this phone as in my view the improvements it offers (greater bass, overall bigger phone sound) are outweighed by its drawbacks (slight muffling and some distorting of high frequencies, and not so suited to slinging in a rucksack). This is all of course very subjective - and above all I would heartily suggest that if you're thinking of getting this phone you either resign yourself to taking a chance (some reviews put it on a par with the dearer Denon AH D1001) or find a way to trial it at and a variety of volumes. Don't do as I did and be persuaded only by listening to La Bamba at full blast in a noisy Apple store unless that is what you're after in phone.