I'll break this critique this critique into five sections which are:

-Anatomy and pose
-Lineart
-Colors
-Lights and Shades
-Overall impression


Anatomy and pose:
The face is definitely the best part here, no question about that. The hair could benefit from some reworking, but it doesn't look as flat as before. However, the coloring has some issues that augments two dimensionality, which I'll cover later in the critique.

The pose is quite solid, although the anatomy requires some attention there and there. I'm most uncomfortable with the way you drew the fist. The way it is now makes it look like it's loose. That's because we can hardly see the arm and the sleeve. Also, it feels like the arm is close to the body, which doesn't look very natural. If you had drawn it in a little different angle and included the sleeve, it would look more like it was "part of her body".

The hand close to us has it's issues, but I find that the arm position behind it more crucial. Or rather, the way the clothing drapes. The drapes around the shoulder, although pretty, don't contribute to the intended arm position. The way it's now doesn't indicate arm coming towards us in anyway. You need to see the form in three dimensions. The draping makes the shoulder look quite flat. The part that's completely behind the hand also has it's issues. Although I understand it's rather tricky to draw from that angle, I would prefer having at least some draping to indicate that the arm is bent.

I find that the area with her collarbones look way too flatter than it should. I believe some changes to the line art would work here. Also the way you drew the shirt makes it the are look rather flat. Pay special attention to the neckline: the clothing, both the shirt and the coat doesn't contribute to the body under them. Especially the straight outline of the coat is a real sinner here.

Lineart:
Thank you for providing me a version with only lineart. Improvement in this part is clearly visible, but you aren't quite there yet. Most of the time the lines are rather undefined and wobbly. They look like you have drawn them slowly in short strokes and then tried to fix them by erasing. The lines are also rather thick in general, and those rare thin lines don't seem to belong there.

I know I have said this before, but I'll say it again: draw quick and confident lines. The faster you do it, the more precise it will look. I truly hope it's not just the issue with your tablet pressure sensitivity.

Colors:
The colors don't quite work, as you have come to realize already. One thing I find pretty good is that her hair color is clearly augmented. The eyes focus there first, which is good, given that you have been most successful in that area in particular. It's not completely perfect though.

I believe it's mostly about the technique you used. The brushstrokes are visible, but they don't look intentional. The strokes are blurry and random. Simplification here with bigger brushes may prove beneficial. I'm not really into painting style, as I don't see myself as a painter, so I'm not one to give proper tips in this matter.

I believe the worst mistake you did here was black color. The shirt is way too black now. It's absorbing all the light. Remember that in real life black doesn't look completely black very often. The black is okay with the lineart, but as a color, it just doesn't work out in this case.

Lights and shades
Turn your drawing in gray scale to see the values. You will notice it's rather plain. For instance, if you look at the hair in this way, you will see there is hardly any contrast there. Have more contrast between light and dark tones. Also you should probably start with lighter base colors.

Remember that you are drawing three dimensional forms. You need to take in account the direction of light and the shapes that are affected. The way you have shaded the drawing indicates that you haven't thought it in three dimensional space. Although the effect on hair is actually pretty cool, it doesn't seem to take in account the light source or forms. You are trapped in two dimensions, which you need to get rid off.

I advise you to make shadow analysing before going with the colors. Have a look at this: [link]. In this drawing, I have used yellow on lit areas, grayish red on areas in shadows and cyan for areas affected by ambient light. Mark the light source(s) with arrow and "scan" your drawing: which areas are lit and which are in shadow? Is there objects that casts shadows on other objects? Is there reflected light illuminating the objects (secondary light sources)? These are basics that you need to know.

Just to point out, be careful how you highlight or shade certain areas. For example, have a look at the belly, the line defining belly and the hips. It looks like it's rather deep scar. This could work for your benefit in some case, but not probably here.

Overall impression:
Each drawing you draw are important to make you better at drawing and this isn't by no means exception in this. Although it leaves a lot to be desired, it's definitely one of your strongest works so far. The pose and the face are the most successful here.

Overall anatomy = well done

Hair flow = good

I actually like the hand in the foreground, I can see what people are saying about the thumb being a tad long. Maybe that should have been scaled down a bit. To be honest though it doesn't bother me, personally.

Now for the coloring:

You might want to consider toning it down a bit. The colors are a bit harsh, a lot of black undertones everywhere.

Maybe you want to try and use a lighter base color, then slowly go for darker colors as you shade.

For example the hair the base is fire engine red. That color maybe should have been saved for the final shadows.

That being said, I'm overjoyed with the outcome, although i'm sad you had to spend your birthday that way.

Can't wait to do another trade with you ^_^