Thanks a lot for the replies and comments, all of you. A lot of food for thought and nice pointers here. I'll be studying the things you all mentioned here in detail once I get from work and have some free time (maybe in the weekend). I'll take heed of all the advice and I'll be sure to post an update to the piece soon.
Just in case, the character is not mine, is Eureka from the anime series Eureka seveN. The artwork is mine, though, I didn't base it on any piece (tracing), I just sketched a rough lineart as in the progress animation.
@Shifty McSly: Yeah, I notice what you said about the neck being too long. I assume Helm also noticed this, because one of the changes in his edit is the neck lenght. I don't really agree about the hands being too small, but I'll be sure to study it more and maybe I'll tweak them a bit.
@Pawige: Yeah, it happens to me a lot. Somehow the rough sketches (be them pixel or traditional pencil & paper) tend to look more natural or smooth, and when I "clean" the rough edges the end result ends looking too stiff or artificial. Still figuring how to avoid that. I kind of agree with you. Even something in her face looked more natural and similar to the character in the sketch.
@Helm: Lots of great advice there. Thanks a lot for the time you took to edit the piece. I'll be sure to inspect it all carefully and take a good look at the changes to see how can I implement them myself and how could I improve on them to increase the quality of the art. Is there possible you could post me some links to good anatomy sites? I tend to use the net to find anatomical references, but mainly pictures. I'd like some sort of theorical approach, you know, to the terms like contra-posto and all that. I've studied that a while ago in college, and I must admit I'm very rusty, mainly because I've stopped practicing my traditional art skills. Bad me, bad me. As for the clothing, well you're certainly right, gotta check out how the fabric SHOULD fold around the body. Even if her outfit is really tight, there should be some wrinkles and all that. As for the colors I sure have room for improvement, either adding or swapping colors. I don't really mind adding some color to the piece, I could even use 16 colors, no more than that, though. Once again, thanks for your thoughtful comments Helm, very much appreciated.
@Ptoing: Heh, I notice what you mean about her looking like in a photoshoot and being uncomfortable. Kinda true. Also, thanks for the comment. I'll be sure to study some more anatomy (gotta admit it's not one of my strenghts, too much anime/comic drawing and too little traditional art studies

) That can be remedied, though, just need to dedicate more time to my art.
@Player1: Although Helm's edit did lose some of the cleanliness (or flatness, as I would rather call it) he has a good point when he says you must sacrifice something to get something else. Still, good comment, about trying to keep the piece clean and smooth and add more detail & fix issues.
@Frychiko: Wow, just a small change on the legs can change the entire piece and that pose also looks interesting. I'm going to study that edit too to see if I can find a balance point in between the original posing and the more balanced one you've made. Thanks for the input!
Well, I'm out for now. Going to revisit this piece really soon and try to improve on it based on all the advice. Thanks!
~K