Not a great pick, not terrible but not great either.
Biden is regarded as being a foreign policy expert because he can name the Prime Minister of France without Google and to a certain extent, relative to other DC politicians, that DOES make him a foreign policy expert. But once you go beyond that, his knowledge and insight doesn't go much deeper than a Wikipedia page.
He's a former chairman of the Senate Foreign Relations committee and was the Obama administration's point-man on Iraq. He would be perfect for the role.