(Cropped the original, since I reworked the girl on the left. See post further up.)
Not having a strong underdrawing for the faces really killed me on this one, especially for the foreground character (NB: Has since been deleted). Took more time than was needed. So as punishment, I redrew her from scratch a few times to remind myself that Photoshop has layers and opacity settings for a reason. These are all purely digital on Cintiq, by the way:
(You can spy the undersketch if you look closely enough. Having this solid first really pays; though I find myself drawing as much on this layer as I do just trying to lay down perspective and anatomy guidelines. This works, but it's partly what killed me on the first pass of the drawing, getting too caught up in details when I should've been more concerned with overall proportions and proper facial geometry.)
Don't be surprised if part of this post suddenly disappears at some point.