Yes, particularly in Godfather II, we rarely see him smile, and he never laughs. (Not that there was much to laugh at). He forced a smile in Havana when he was jokingly told that one of the politicos does a mean samba or cha-cha. His relationship with Anthony is cold and distant. His mannerisms and expressions were frequently lifeless, but maybe it was his attempt to follow Vito's advice of never letting anyone know what he was thinking.
If only Sonny knew this.