Zombie Apocolypse

Not bad at all, I like the environment and setting, though I feel it could benefit from some spookier lighting to bring out the foreground models and areas of interest, maybe dim red/orange dawn or dusk, or even eerie white moonlight that casts sharp black shadows.

The pastel 'sickly' purple in the sky and around the image actually works nice, I just think there needs to be more contrast on figures against the background; so imagining them as graphic shapes, you can choose to make them more silhouetted against the backdrop with parts of them slightly illuminated (like a band or tip of light across her forehead/eyes while her lower body is cast in shadows)

Or illuminate the foreground models a lot more and have her entire upper body banded with light, and the zombies have just tips or parts of them showing in the light.

Lighting is probably the hardest thing I'm still getting used to, but just trying to help out with some of what I learned while doing formal 2D stuff. I've noticed when dealing with 3D it helps to put up primitive shapes off-camera to partially obscure or block a ray of light, which can allow you to get some nice dramatic lighting; like a building or object is rising up off-screen which can compel the audience to use their imaginations more too!

I really like it BUT... Contrast is your friend if you want an aspect to stand out, very much like @illithod said about lighting. If you need to, just think about it as the final product, you've got a woman with dark hair and dark clothes on her torso but the background is also dark so nothing stands out. Putting a lighter object or some light to pick out the shape of her body will make the figure 'pop' as the main subject.