I'd steer away from gradients and solids, in the capactiy that you're using them here, get some texture into your environment. Work on getting the city and buildings a little less symmetrical looking and more gritty/dirty with shadows, highlights and all that, even shadows and lights of things that aren't in the picture. But mostly I'd encourage you to work on the anatomy and pose of your person; try to picture what someones body would do if he was leaping from rooftop to rooftop, the way his body works when jumping in that manner. Look for some references of a person leaping to help you out.
My two cents.