i can see that a lot of time and effort went into this. but to put this bluntly you're lacking in fundamentals. the character is stiff. you should look up gesture drawing. Your line art is super boring which can easily be fixed with a change in line weight. look at my stuff for example. (im not the best tho) dont be afraid of other colors. the shading. pick a light source, remember that objects cast shadows. there should be hard shadows too. the airbrush is not always the right option for highlights, and lastly there should be more contrast between your base color and shadows. (that means darker shadows). Good luck with all your other art ^_^

I'm not sure why the rating is mature, but I like the right arm and other implied cyborg or techno parts.