I like what you've got going on, generally. As to the girl image, you have to take anatomy from the top. Kon's edit is helpful, but mimicking it will not be. Take it from the top. Take fine art classes, draw from models or reference... otherwise you might get to be a very strong pixel artist, with no real life skill and that will always show in your pixels.
About the face now, I like the few colours, and whereas I was tempted to add more for my edit, I stayed with the GBness of it all, heh. Problems:
*Your black lines are jaggy. You antialias them sometimes, but they're still jaggy. Usually black lines shouldn't be jaggy.
*Just because you have few colours doesn't mean you shouldn't try dithering... I like the posterized effect myself a bit, but give other things a try. I did a small Pep-style attempt, but not fully, as it would take too much time.
*Don't copy reference too exactly. Your pixels shouldn't strive to be like reality when you work with 5 colours. Change things, even if they look realistic. Make compelling images. It's too easy to get trapped to copying from reference too obsessively. Let it breathe a bit, add stuff that looks good even if it's taking a chance.
*Antialias uniformly. For 5 colours, this is a must. Generally, antialias like a machine. The places you can do this are so few and always the same, you can do it pretty much automatically. Selective antialiasing (and buffering) is a matter of having 2-3 buffers between two shades, not one or none. There's a lot of places you didn't alias at all, and it looks.
That's it. I like the colours, I like some pixel techinques. But your lineart skill suffers. Focus on that as much as you can. Take a fine-art course, or pick up a good book or two and hit it with all you've got. You might progress without doing these things, but oh so much more slowly.
Kon: your edit need about half a head more of lower leg, and better curve adjustments.
