Obama's legacy is that he was the first black US President.  Whoohoo!  Look, he got into Harvard on affirmative action, and basically became the President because of affirmative action.  It proves that the US is not a racist society, on the whole

As for policy and effectiveness, he was a total failure and leaves America more divided than at any time in the last 50 years.  On the global scene, the US is at its weakest position since the Carter years.