welcome rob! those concepts are gorgeous, and these sprites really do not live up to them. You've got a lot of jagged edges in both your outlines and your shading, the hair is not faithful to the designs (maybe put those swirlies at the end back in), the skin is shaded more harshly than the giant refueling device (which is metallic i assume?), and the legs in the run animation overlap quite a bit!
You have some crazy talent, I would revisit these with a few things in mind:
1 - Planes/depth/contrast - in pixel art it can help if you use darker colors to help cue the depth on your character. E.g. make limbs and accessories that are away from the camera darker than the parts closest to the camera. This is not like a "rule" or anything, I just think it could help this particular sprite to read a little better! A lot of the street fighter games do this to great effect.
2 - Cleanliness - take the extra time to clean up your lines and smooth out your shading - make every pixel count!
3 - Don't be afraid to animate whole new frames, instead of just sliding bits and pieces around. In fact, I'd block out your animation frames first in lines, then in solid colors, and then keep on tweaking that super-simple version of your motion until you're happy with it. THEN go back and start adding details!
Again, welcome to the boards, congrats on your killer 2d skills, and I look forward to seeing your updates!