It is by sheer technique a really good piece, but the main problem with it is the lack of difference between each Sin sans Wrath and Gluttony. The lack of variety is the downfall of this piece and if you ever returned to this piece or similar theme, more variety would be in order to increase the impact. It's difficult to distinguish Pride and Envy for example - they are drawn only with some differences. Another problem that inhibits the impact of your vision so to speak is the lack of variation amongst facial expressions that the Sins are showing.
The prime improvement that can be easily achieved is more diversity amongst the individual design for each sin. The symbolism connected with each sin could also be elaborated upon, making it more distinct or indeed visible - you use them yes, but they aren't always obvious to all. Greed as such is indeed a prisoner of his own desire but is it obvious on the first glance what it's referring to? Probably not without being used to looking for metaphors in art or literature they come in contact with.
Oddly enough, the women for lust is slightly out of place - if not for pride's placement, she would become the focus of the picture by the virtue of being unique amongst seven angels - even then, she still draws attention away from the theme of the art. On the other hand, Gluttony by far is your best character design on the flip side - it is distinct enough without extreme reference.
Your technique is something I would envy were I a artist ... it is in fact brilliant. I have to say it makes the impact greater than it would be otherwise. Your drawing style as well as the actual colour filling was very good indeed, which leaves me nothing to pick at - sans you alternating to a different style slightly, I can't help you there.
The idea itself is rather original as most people do not create Seven Sins as angels, but rather normal humans, making your concept fresh in a sense.
Also, Deathstars are awesome. Did you like "Motherzone"?