With their tight fit, the earcups do manage to seal out a decent amount of sound, and I thought they were pretty ideal for my commutes on the New York City subway. When faced with a lot of ambient noise, it's better to go with headphones that push out more bass because that external noise can end up muscling out lower frequencies.
Aside from comparing these headphones to the ATH-M50s, I also put them up against the Creative Aurvana Live headphones, which list for $99 but can usually be had for less. Though the Creatives don't fold flat, they're clearly more comfortable and also offer excellent sound for the money. I did think WS55s' bass had a little more punch to it, and I'd say the WS55s come out on top in terms of overall sound quality, but just by a touch. (Of course, sound quality is very much a matter of taste, so your opinion may vary from mine.)
The ATH-WS55s deliver excellent sound for the money, with tight, punchy bass that's matched with refined midrange and treble performance. They're not quite on par with Audio-Technica's more expensive ATH-50 headphones, but they're lighter and more suitable for mobile use.
The only strike against them is their comfort level. I wouldn't call them uncomfortable -- and naturally they'll fit some people better than others -- but their comfort rating simply doesn't match their performance. My advice would be to buy them at a place where you have the option of returning them should you not like their fit. But aside from that caveat, I can strongly recommend them.