Pros: Build quality, design, sound quality
I will first start by declaring that I'm no audiophile, and that this is just a review coming from an average consumer. I know a lot of you will facepalm by my review, but I will post it anyway.
One year ago I bought the ATH-M50, coming from a Beat Solo HD headphone (yeah, I know). Although the Beats and ATH-M50s were at approximately the same price, I was simply stunned by the open sound, the tight bass and crisp sounds from the ATH-M50s. However, after a year I thought it was time for a new upgrade, and doubled the budget I had one year ago to £250. After I had bought the Momentums I excitedly went home expecting I would get the same WOW-feeling as I had gotten from the ATH-M50s, but when I plugged them in my computer and put them on my head I was just surprised. Not because they sounded good (they did), but because of how average and familiar they sounded. They sounded almost like the £100 cheaper ATH-M50s. I tried connecting the Momentums to the cell phone and the iPad (the box says they are "made for" iDevices). For three hours I listened to the Momentums, but after switching over to ATH-M50 right after I still heard no big difference. Disappointed I returned them to the store and once again I'm looking for a new pair of headphones.
Some might say I wasn't satisfied with the sound because I was used to the ATH-M50s, but how is it a matter of taste when they sound basically the same?