I think the overall likeness could do with some work yet, some general advice: I've done a fair amount of portraiture, and I'd say it's helpful to
overstate distinctive features, to the point of caricature and scale back if needed; it often isn't.
Big things: he had tiny shoulders; he's a fairly chubby guy, I also think you've lent him far more neck than he credits

.
Smaller things: I actually thinned his face slightly for proportion, he lacked a top lip & I think his whole mouth area is actually quite characteristically smaller and more puckered. Your eyes & brows pulled down at the corners which I couldn't see at all in ref; larger, lighter ears, more amusing hair.


Edit - yeah, went overboard on the shoulders.