after listening to the momentum in ears for about a week or so,
i think sennheiser has got it right on a lot of fronts!
firstly right off the bat, they were very comfortable (a combination of the angled (and slim nozzle) and the rather small footprint (the shape is a bit irregular, but at the same time still very ergonomic), without adding any bulk (even though i recall, sennheiser stated that they have a metal body) the outside shell does still appear to made of glossy plastic (i have the chrome/ grey version)
i liked the cable on the sennheiser cx 3.00 & 5.00G as well, and sennheiser carried that over to the momentum in ears (having a eliptical cable) without being too heavy (cable noise i found is fairly minor for the most pair, which is not always the case with "flat" cables usually)
soundwise, its bassy (but not overboard in the bass i found), i found them closest to the Brainwavz S5s (about the same price point) (but i found them a bit more refined in almost all fronts). THIS was BEFORE i looked at the measurements!
the s5s does appear to have more impact in the bass (especially in the midbass) but it does sound noticeable boomier.
midrange both take a back seat to the bass in the treble
treble wise the s5s seems "edgier" and a bit splashier (a sentiment some including myself shared in the S5 reviews), while this made them more energetic and "fun"
the momentum in ears seem to capture a lot of that "fun" while at the same time smooth out the edges (making it less grating on the ears), but avoids sounding dull like on some bassier headphones.
i think acoustically its a step up from the similar priced (and sibling) the Sennheiser cx 5.00G (its more detailed and better tightly controlled)
so far i would put it on a similar tier as the Alpha and Delta Ad01, and the Nuforce NE800m (both bassy but are both one of my favorites), with its tuning being slightly closer towards the AD01