Here's a few things I see about your art that seem to come up every time.
1. From the value range that you have available, from 0,0,0 black to 255,255,255 white, you seem to work in the middle upper register. You have very many near white colors and usually just black, a close to black and then huge jump to middle shades. I think the human eye is more used to see hue variations in low middle shades, which is where most master painters worked too, with strong and defining hue jumps towards highlights, and shadows the melted towards a grainy gray. I don't follow this idea to the letter (I have a propensity for saturated near-blacks, personally) but it's a valuable thing to consider, how you're effectively *straining the eyesight* if your viewer with all the near colors in the higher middle/highlight range.
2. At the same time, on your lower values where black lineart turns into a sculptured object, there end up remaining single pixel or two pixel clusters of black or near black that make the lower end of your image look EXTREMELY SHARP. This effect couple with 1. above makes your art have this unpleasant - to me at least - effect of a botched photoshop levels/curves middle point pass. It misses the valuable middle-low register in the values but yet the black is punching and sharp and there's a multitude of whites. Are you aware you're doing this? Is this a conscious choice?
3. On a straight pixelling related point, single pixel clusters or two pixel clusters, when used so much and so prominently (because your black and near black is so far away from the next shade) they read as specks, blemishes and/or noise. This is something to consider regardless of the color and value thoughts above.

Your latest.

Contrast & color photoshop pass

Careful pixel level edits and manual color calibration pass.



I don't know if you do this, but I suggest you look into the edit in your paint program, flip between the two frames (this is why I put up animation flips usually) because there's lots of suggestions on the nitpickery level as far as facial features and shading go.