It's a really good render!!! As for the shape of the guy's chest, I would go for a more squarish shape; it makes it look more like muscle and less like fat. And I think you chose very saturated colours for the shadows; maybe use a less saturated shade for the darkest tones.
thanks for the feedback! may i know how you go about choosing the saturation for shadows in general? I kinda just pick the colors at random since the values somewhat permit it, but colors that are closer to realistic would be cool to know.

