Lack of colour
Is what is killing you work. VIBRANT!!! We want VIBRANT!! or some colour theme. No more "just white". Ok? You draw manga you say? Well, (this is just my opinion) your eyes, slightly too big. Needs more of a nose, and well... shading. Shading. Manga artists don't really colour to much, so if you're bad at it, I don't care. You need some shading to finish this up, as well as geting rid of all that white.