You need to go back to the thumbnail phase. Do very simple thumbnails with just a few tones.
To help you, read these first:
Composition Basics: Value Structure
Composition Basics: Sketching Thumbnails
The Thumbnail! (by Jon Foster)
In the second article, Dan says:"You can stop here" and this is what you should do. You want very fast thumbs, no bigger than a business card (mine are usually even smaller.) You can do them digitally, but I thumb in pencil in a sketchbook.
If an image works when it's very small, 92.6% of the time it will work when it's bigger. The few times it won't will be because you borked the anatomy/perspective and the thumb was too small for you to notice. But that small percentage is not a reason to not do thumbnails. Everyone who is good does thumbnails for finished pieces, and it's not because it's hip, it's because it works.
The specific problems with your image is that the figure in white is completely straight, it doesn't look like it has any momentum. If the darker stuff at the bottom is the ground, then his legs are way too short. He has a cool rendered head and ear but the rest of him is not legible. The robot thing flying away looks like it was straddling the guy in white before being punched. If he's overlapping because he was in front of him and his now flying away, the angle of the punch, the perspective on the guy and the amount of overlap don't fit. Now, overlap is good. Overlap is dynamic, we want overlap, but the elements all have to work together to make the image stronger. If the overlap doesn't fit the perspective, something has to give.
This is why thumbnails are important. I'd say you need to do at least 12 of them for each image. Some art schools have their students do 50 thumbs for each illustration, it forces you to think really hard about what is important in the image and find new interesting angles.
