I think your strongest point in this shot is definitely the composition of the shot. The way the you use the depth of field in this shot helps emphasize the focal point, which appears to be the two boy's hands holding, in an arm wrestle. The contrast in this image also helps create some tension, and the the eye contact made with your subject emphasizes this. The light in this shot is great as well, as you have plenty of detail on both faces. There's only a bit of detail missing in the boy on the right's hair. However, I agree that often shots have more impact, depending on the how light and dark you choose to make them. The tonality in this shot helps emphasize your shot even more, as the lightest parts of your shot appear to be located on your subjects hands. Overall, great portrait, and creative too!