While the HD 238i headphones don't isolate noise as well as over-the-ear models, they do well to muffle outside noises -- this is called passive noise cancellation, in contrast to the active noise cancellation of some headphones that requires an internal battery to work.
In reviewing the Bose OE2i, I noted that they sound more natural and don't suffer from "Bose bloat," a term coined for its obtrusive bass boost. These Sennheisers exhibit similarly detailed sound and ample but not "bloated" bass. These are a touch on the warm side and will appeal to listeners that prefer more laid back, less aggressive headphones with edgier treble.
Keep in mind that you shouldn't expect the same kind of sound from these Sennheisers as you would with higher end models that cost well over $200. The point here is that the while the 238i's don't offer great sound, they do deliver very solid performance for their price.
The Sennheiser HD 238i headphones actually carry a list price of $169.99, $10 less than the Bose's list price. Bose headphones are very infrequently discounted, however, and a quick CNET Shopping search finds the Sennheisers for around $130. (Note: I saw them for as low as $57.64 with free shipping, but after this review appeared, CNET readers quickly gobbled them up and vendors raised their prices).
No, they aren't quite as compact as the Bose OE2s and they don't stow away into a small carrying case, but they cost significantly less and offer comparable sound quality. In my book, that makes the Sennheiser HD i238i one of the better bargains in this class of headphones.