I dig those elephants, the fish, and the robots.
The zombie sketches aren't bad, but could be better. It has too many hard edges that don't mesh well with your overall softer rendering style. Don't fear your eraser. Use it as another drawing tool. Soften those edges, have them disappear into the shadows and have them come out full force in other areas. Even using the same shapes (which i didn't normally think could be appealing, but here i see the potential for an exception), I bet you'd get more visually appealing drawings that way.