I don't do much animal photography but looking over this image something strikes me. The natural camouflage of most animals is one of the features that makes photographing them with contrasty backgrounds so difficult. This deer's coloring is subtle and without much natural contrast. The background however is very busy. Not that one has all that much control but if the animal could be isolated with a shaded background that might help. With backlighting I'm not sure how to make him stand out more. Your lens seems sharper at mid telephoto.
