Ok, I can be a harsh jerk, so let's begin.
Firstly...the important thing about eyes is you need to have the same impression from both eyes. That is unless your character has two different eyes, which in most instances is not the case. The reason I point this out is because your first sprite, the little dude with the white helmet and gold decorations, has slightly inconsistent eyes. The left eye's highlight blends in with the outline, which gives the impression of a different style. Try and "balance" both eyes so they look even. Your megaman sprite has quite well balanced eyes, so take that as a reference point. Sometimes it can be difficult to get the effect necessary, and you may have to get creative.
I don't quite understand your shading -- some sprites have shading in places but in other areas they do not. The birthday girl does not look shaded at all. In sprites that you have shaded, you have shaded only some of the areas that need it, while other areas are left unshaded. I am making this judgement based on the style it seems you are trying to go for. Take megaman for instance. The left part of the chest is shaded(?) but the left arm and leg is not. Your opening sprite (with the helmet) is shaded on the right side everywhere but the face, where shading may be most important (given curvature of the face).
Birthday girl's background is a bit too bright, try a paler pink. I would also recommend anti-alising the cake stripes as they look a bit jagged otherwise, which doesn't match the clean lining style you have elsewhere. Just pick an intermediate colour between the stripe and adjacent colour and put a couple of pixels at the end of each "step".
Besides that, you have a really good grasp on shading and the style is good. Just need a few tweaks here and there (as we all do!!).
Firstly...the important thing about eyes is you need to have the same impression from both eyes. That is unless your character has two different eyes, which in most instances is not the case. The reason I point this out is because your first sprite, the little dude with the white helmet and gold decorations, has slightly inconsistent eyes. The left eye's highlight blends in with the outline, which gives the impression of a different style. Try and "balance" both eyes so they look even. Your megaman sprite has quite well balanced eyes, so take that as a reference point. Sometimes it can be difficult to get the effect necessary, and you may have to get creative.
I don't quite understand your shading -- some sprites have shading in places but in other areas they do not. The birthday girl does not look shaded at all. In sprites that you have shaded, you have shaded only some of the areas that need it, while other areas are left unshaded. I am making this judgement based on the style it seems you are trying to go for. Take megaman for instance. The left part of the chest is shaded(?) but the left arm and leg is not. Your opening sprite (with the helmet) is shaded on the right side everywhere but the face, where shading may be most important (given curvature of the face).
Birthday girl's background is a bit too bright, try a paler pink. I would also recommend anti-alising the cake stripes as they look a bit jagged otherwise, which doesn't match the clean lining style you have elsewhere. Just pick an intermediate colour between the stripe and adjacent colour and put a couple of pixels at the end of each "step".
Besides that, you have a really good grasp on shading and the style is good. Just need a few tweaks here and there (as we all do!!).