He just doesn't stand out.
It's good but it's too cluttered, I find this with a lot of your artwork. Try to not detail everything as much as you do, like backgrounds or floors. The problem I have is if everything is as detailed as Bomb Boy, how will Bomb Boy pop out of the poster? He is the centrepiece after all. Maybe make his lines thicker, or change his or the backgrounds colour because he's the same colour as it. Experiment with blank space.
I'm not sure if you're making a game or not, if you are, I'm looking forward to it!