if you want to detailed critism, i will go for your latest artwork...
i see its pretty smooth and neat, and detail for line art.. im using different method for design so i think draw line art for this is pretty complicated...
second is about shading... i'll take your gintama draw, you should choose between drawing relistic or manga-ish style... that will determine the method to do the shadow... your shadow is too smooth and too transparent, i can barely see your shading, need to detail more, and deepen the value...
seems this is it
... hope it can help you improving...
come to my stream if you want to see how i shade things...