Well, to be honest, you should increase the lighting a little bit more in the other side.
The tree looks so dark and I recommend for a little bit of lighting to be placed to make the scene a little bit more realistic.
This GFX does look amazing so far, but I find a few things wrong with it that would really transform it! The first thing I noticed is the weird shading effect on the hat.
I’m not sure what program you used but that weird effect does happen with Blender a lot. If you did use Blender. This can simply be done by finding the Object data and if auto smooth is turned on, turn it off.
Also some of the shadows are slightly confusing, it seems the light source is coming in from the left side of the image, but there’s still shadows underneath the zombie.
In my opinion it just confuses the viewer, and clashes with the light effect you seem to be going for. On the topic of lighting it looks too bright in some areas, I’d tone it down a little and remove the funky shadows underneath and around the avatars. Also I would remove the glowing effect on some areas of the avatar? I’m not sure if that was edited in after the render or if it’s the lighting being too bright, but it sort of clashes with the extreme shadows.
I hope my advice helps you out in the future! I tried to be as constructive with it as I could but it’s kind of hard not knowing what program you used. Other than the few things I didn’t like it looks pretty good none the less!