Well, they mostly look flat because of the cell-style shading. That's not necessarily a bad thing, but does tend to be a rather flat style.
Not sure if it was intentional, but it looks like in the second example, she's only shaded from the waist-up. I also notice in both of these, there isn't much shading going on around the face. For instance, in the top example, bottom right head, there should be a little bit of shadow along her jawline if the light source is coming from above. I do like the highlight in her hair in both the full-body examples. I would suggest making sure all parts of your character are shaded/highlighted in accordance with the same light-source, or else things can look a little wonky.