I agree that the build quality feels cheap, but it's actually come to be one of my favorite parts of this headphone. They are so light, and the entire design is just the minimal amount of materials to hang the drivers next to your ears. They just disappear on your head after a while, which combined with the great soundstage provides a wonderful experience.
I don't find these cans to be bass light at all. Although they certainly have less bass than my D2000, they have great impact with no boominess. In terms of measurements, the bass is slightly boosted above flat (
http://en.goldenears.net/14492), but I actually think this is necessary for headphones as opposed to speakers to give a natural presentation. The bass quality is great for me; I tried the mad dogs with alpha pads and the bass was too tight and lacking in quantity, to the point that a bass drum didn't sound the size of a bass drum. The sony's lost slightly on bass texture, but in overall naturalness of the bass, they certainly won.