Pros: Soundstage, comfort, midrange, bass
Cons: Little dark (for my tastes)
Ill make this short and to the point.
The MDR MA900 is a fantastic headphone and even fantasticererer at the price of $200. The soundstage is just unbelievable, trumping cans that cost more than twice it's price (HD650, HD600, DT880). The imaging is also great, and the best thing about the soundstage is how focused it is. Neither the vocals, nor the bass are lost in this soundstage (amazing!).
Let's take a break from the sound.
These are hands down the most comfortable headphones I have ever worn, so if your thinking about the comfort, just stop it because it's just silly. I read someones impressions somewhere and he described the comfort as it being like a hat: after a few minutes, you forget they're even there.
The build is... well the materials themselves are good, while also keeping the actual weight of the headphones very low, but the structural design has its flaws. Dropping these is ok, but sitting on them, won't break them, but it may just mess with the swivel mechanism or something of that sort. The headphones actually look nice, but are not very inspiring when you have them in your hands.
Sound: The mids are very clear and the instruments sound true to the source. The bass is surprisingly good. EQ makes the bass actually better than a lot of other closed cans at the same price. On it's own, and this is just me, it lacks impact for pop, hip hop, and r&b, but its great for rock, jazz, etc. The highs are slightly recessed (EQ to the rescue).
Overall, they trash every closed can I've heard (and that's without an amp).
This review was done without an amp.
9.9/10 because of the look.