Pros: Tonal balance, light weight, durability/serviceability, low-key aesthetics
Cons: Smaller/shallower soundstage than a good open-back headphone; may require some break-in time for optimum wearing comfort
The problem with having a reference-grade pair of headphones for home listening (in my case, Grado's amazing Prestige Series SR325is) is that when you start looking for 'phones to listen to away from home, just about everything you try inevitably comes up short in one way or another, and the name of the game becomes "which set of compromises am I willing to live with?"
For me, the current crop of headphones aimed toward portable listening is, at best, merely acceptable. I could drag out the usual suspects to use as punching bags, but we already know who they are; just think style-over-substance and there's no need to name names. But there are a few seriously-mediocre 'phones out there offered by outfits that should definitely know better (AKG, I'm looking at you). Really, nothing I listened to in the "portable headphones" category did the trick, which is rather astounding given the money being asked for some of the upper-end models.
Then, while grousing about this situation to a sales guy at the headphone counter at J & R the other night, I got a suggestion I should have thought of before: ignore the "portable" category altogether, and audition something a pro would use. However, one good reason why I hadn't thought of this is that most "serious" headphones also typically sport some serious size and weight, and aren't always something that's easy for something like an iPod to drive at satisfying (not ear-splitting) sound levels. Yes, wearing big 'phones on the street is apparently cool again, but I prefer being a bit more discreet in my headwear, although I'm about done with in-ear phones and their assorted anomalies.
The sales guy then handed me a pair of these Sennheisers. I listened. I looked them over. I listened again. I was sold, simple as that.
They're decidedly ordinary-looking, literally dull. Sennheiser didn't exactly go out of their way to make an unstylish headphone: this is a model that was pitched initially to people who care a lot more about a 'phone's performance and reliability/durability than about how cool they look (or think they look) while wearing them: recording engineers and producers, sound-reinforcement people for the stage and the screen, sportscasters, and, of course, DJs. Think of the '55 Chevy James Taylor and Dennis Wilson drove in Two-Lane Blacktop: not slick, not working too hard to be cool, but clearly having what it takes to do the job.
And, what a job! Riding the train or bus, or walking the streets, I get the music, full, deep and wide...or not, depending on the recording. Being more of a true "monitor" headphone, the HD 25 doesn't do much in the way of juicing or monkeying around with the signal in the name of making a grand impression; if the recording is good, you'll hear just how good it is, perhaps for the very first time while away from your "reference" home 'fi. If the recording is sub-par, you'll know that, too, but the result won't necessarily be unlistenable, just minus any sugarcoating.
A few have pointed out the HD 25's nearly all-plastic construction, regarding it as "cheap." There's nothing cheap about this headphone's materials or construction: having been on the market for well over a decade, its design and build quality have been proven countless times in the professional field, where people are not known for treating gear with kid gloves. In the hands of the average consumer, these cans will easily outlast any flavor-of-the-month style-phones by an order of magnitude.
As durable as these are, they're also a damn sight lighter than your typical please-don't-drop-me bling-phones. I won't say it feels like you're wearing nothing on your head, just that it's a light touch overall. For some people, however, the pressure of the headband's "clamping" effect might be a bit much for listening much beyond an hour; this gradually eases as the headphones are broken in.
And, speaking of "broken": if by some freak event you manage to do damage to any part of the HD 25, that broken part can be replaced; Sennheiser keeps an inventory of spares if needed.
(As an aside, these headphones happen to be manufactured in Ireland. Take away what you will about that.)
That's the picture for you. I love the things. I think there's a fair chance that you'll at least like them.