I believe you are going the wrong way in trying to improve your art. You are trying to fix fundamental flaws in it by applying some automatic post process effects, and that will simply not work. The underlying flaws will still remain, doesn't matter what post process you use.
Please don't take personal offense, but your style reminds me of someone who learned how to use a graphics software and still doesn't have matured enough it's artistic skills. It looks a lot like some graphics from the 90s, that in todays standards seems a bit cheesy and outdated.
In your current attempt you tend to overuse gradients and effects, use to much pure colors (full black, full white and pure RGB colors), and are not very fortunate in establishing priorities within your scene. The danger sign that is supposed to be a detail in the background have as much highlight as the characters (if not more). The characters doesn't have enough contrast with the background, and their instances seems a bit stiff. Everything is so high contrast that looking too much time to it may give the player visual fatigue.
I think that if you went with a more comic style with flat colors like your avatar, the result would be much more pleasing and interesting. Maybe Comix Zone may be a good starting reference.
I suggest you try to find more references of styles that you like, and then take some time to study them and rationalize why they work and what aspects are the most important to convey their aesthetics and to make them look good. Then apply your findings in your own art asking feedback to players. If you are too short on time, then maybe you should consider hiring an artist to help you in your project.