One of the best I had so far.
Pros: Not too expensive, Flat, nice build quality, good bass
Cons: The materials are cheap, sharp treble, these cans are huge, not very portable if you want to use it outside.
So, I bought these during my birthday, though I first thought of buying the 688B and I thought the headphones were the size of a small pair.
But I was wrong. Instead of an HD668, I bought these. A really big pair of cans that you can't take out of a studio or a house.
Anyway, the first time I wore these, I already liked them. Though it takes some time to getting used to if you're used to small sized headphones or if you're not used to a sharp treble. You'll get used to them anyway.
For the design, it looks quite plain, it's just matte plastic lolz, matte, cheap, plastic to be exact. 
Though this may be the case, the build quality itself is quite good actually. I've dropped it, abused it, and threw it at places and even bring it to school in a small bag.
So overall, I recommend these headphones to anyone who wants to enter the world of good audio.
UPDATE:
Broke after some time, I guess it was because I dropped it too many times. Though I have to find a way to put back the driver unit back in its place and replace the cord.
But still, I'm happy with them. Bass is somewhat subdued but still present. Highs and mids are very nice. I am listening to them now with a portable amp, tcg t-box, and they have benefitted from this. They draw me into the music. Yay,