Hiya, found this through random browsing. Hope you don't mind a few comments
First, this is a darn good piece of art. I can tell you took steps to avoid giving them all the exact same face or body like so many other artists do, even the professionals! You have very good attention to detail, and your line-quality is top notch!
That said, there are a few things that could be improved, or at least watched out for in future pieces.
1) The head sizes. This one kills me a lot, so I'm in no position to say much, but the heads are noticeably a touch too big, particularly Power-Girl's. The hair might just be really poofy, but yeah, they look just slightly out of proportion.
2) Colors. This one I'm torn on because I'm not sure how it would affect composition, but did you consider using different skin tones or different shades of blue/red/yellow to differentiate the characters more? On one hand, it'd be a bit more realistic if they weren't all using the exact same colors... on the OTHER hand, using the same colors helps pull the piece together, keeps it simple and is more like what you'd see in an older comic book when producing different colors was more expensive. Still, the color sameness makes some elements bleed into one another, like SG and PG's capes, PG's gloves into the other's arms. You've used shading to circumvent this, but a part of me is curious as to what a bit of diversity would look like...
3: Stargirl's right-most hip doesn't line up with itself above/below her belt. Oops!
Over all though, a great piece of work! I love the coloring, it's very subtle, yet rich and complex enough to add necessary depth. The background is also very well done yet doesn't detract from the women. If the rest of your gallery is this good, you'll have earned yourself another watcher!