Summary: I have used a few pairs of Sennheiser HD280's over the past several years, and in comparison, the sound quality of the Momentums is sadly disappointing. Bass is muddy, and the overall sound is colored and more distant, tin-canned, and much less "up-front-and-center" like you'd expect for the price. That combined with the ear cup size -which works great for my wife's ears- really killed the deal for me.
Pros: They look great and they fit my wife's ears perfectly (too small for mine). Works great with mobile devices. Comes with a really solid storage case.
Cons: Price, over-colored sound, poor low range definition (although plenty of "booming" bass which is very muddy), and very small ear cups for an adult male.
Summary: I bought them one month ago... and at the beginning I was not impressed about their sound - they don't seemed very clear and the bass was just not right...
BUT (even I don't believe too much in burn-in), after one month of use almost every day, they are now much much clearer and the bass was also improved (but still not very good in comparison with IE80 for example).
Pros: very comfortable, minimal sound leakage, good passive isolation, very good looking, premium materials, very clear and warm sound, good soundstage
Cons: bass is not punchy and does not have personality
Summary: I have owned both the Black and Brown versions since November 2013 and I am happy to say that they are among my favourite go-to headphones for outside/portable usage. I use a custom replacement cable that is silver-plated and has gold-plated connectors but has the same length as the original stock cable.
Pros: Great bass delivery , Durable and sturdy design , Great noise cancellation , Great color scheme , Includes carrying case
Cons: Over-ear becomes On-ear for my ear size , locking design , iPhone remote cable , not gold plated connector