Here's an interesting first-person account of Joe Biden's foreign policy knowledge and skills from the former ambassador to Romania:
On the 20-minute drive into the city, he quizzed me on Romanian attitudes, the status of various government leaders and the inside story on Romania’s foreign policy toward Slobodan Milosevic, who was still in power next door in Yugoslavia. Because Biden has known all the major Romanian leaders since the dictator Nicolae Ceausescu, the questions were Ph.D. level, not Romania 101. That was remarkable in itself since he is no specialist on Romania; he could do the same, landing in dozens of nations around the world.
In his meetings with President Emil Constantinescu and others, he thanked them sincerely for their support for NATO and then he drilled right in on Milosevic: How strong did they think he was in Yugoslavia after the war? How did they evaluate the various leaders of the democratic opposition there whom he asked about name by name, since he knew each of them personally, too. Unlike the Bush administration, which has been accused of tailoring its version of the facts to match its policy, Biden was trying to learn the facts firsthand to figure out what would be the right U.S. policy.