Tone down that slight BrowRidge effect at the top of his nose. Tweak the eyes just a little larger & a touch closer together. Raise the lower eyelids into a slight wince, puff them out or apply shading to suggest bagginess. You'll notice his eyes are nearly flat across the bottom lid, but the upper lid curves quite a bit. Tweak the corners of the mouth into the permanant smile he always has (nearly a smirk). Chisel deeper forhead lines & move them closer to his eyebrows. Clean up the upper edge of his eyebrows. . . (Well you did ask) :) Actually a promising WIP. All I'm suggesting is a few tweaks. Alternatively - find a really good caricature & exagerate the features that make it so good.