You're relying too heavily on the lines to shape the muscles. Use your shades to build form. The colours are pretty boring, try shifting the hues a bit more and desaturate the shades and highlights the mid-tone is usually the most saturated. You've pillowed shaded his shorts. You're inconsistent with the light source in some places. such as the leg and the abs. I suggest just changing the light source to from the top anyway. It makes it easier to pixel anyway since you can just flip the left and right sprites and say they're different.