I'll let those more expert in domestic politics speculate on the final debate's impact on the election and comment instead on what it might tell us about the future of American foreign policy. To me, the two most notable facts in that regard were Gov. Mitt Romney's decision to embrace President Obama's foreign policy course and President Obama's repetition of his relatively hard line on the Iranian nuclear program. The first suggests a Romney victory might bring more continuity than change, and the second suggests an Obama victory might bring another Middle Eastern conflict.
Although foreign policy has played a minor role in the campaign so far, Governor Romney has consistently taken a hawkish line on it, trying to prevent being outflanked on the right during the Republican primaries and attacking the Obama administration from a generally neoconservative position later on. Beyond his harsh tone, however, he has offered few details about just what he would do differently about specific issues.
During the third debate, he dropped the harsh tone and continued to avoid spelling out alternative policies -- even going so far as to agree explicitly with the president on Syria, Egypt, Afghanistan, Iraq, drone strikes and other hot topics. He reiterated his position about his refusal to accept an Iranian nuclear "capability," as opposed to the president's refusal to accept an Iranian nuclear weapon, but did not make a big deal out of the distinction or suggest that any significant consequences would flow from it. Anybody trying to predict a Romney foreign policy is thus left with lots of contradictory tea leaves to read, which might just be the point.