Any question which asks about the future requires speculation. We cannot know the future until it happens. Moreover, there is no such singular thing as "history" which judges people in certain ways; that is a popular misapprehension. There is no individual named "History" judging people, merely individual historians interpreting available evidence. If we look, for example, at the reception of Pericles, an important figure from classical Athens, we find that different writers over the past 2000 years have had different opinions about him. Similarly, in the future, almost the only thing we can predict with some certainty is that different historians will evaluate Obama's presidency in different manners. Most will probably mention his being the first African-American president as an important landmark in the history of US race relations. His efforts to reform US health care to something closer to the OECD norm may well also be mentioned, probably with approbation by some historians and disapprobation by others.
I cannot help but feel that much of this is going to depend on the results of the upcoming Presidential election. There were some significant moments that historians will look back on with the President as part of his legacy. I think that being the first President of color in the history of America is going to be part of this historical narrative. Simply put, textbooks that display pictures of American presidents will show a different face with President Obama's inclusion. Certainly, little progress on the President's historical legacy can be made without including the passage of the affordable care act. It was polarizing, but represented something that the President held passion towards. If it is deemed unconstitutional by the Supreme Court and/ or if the President does not win reelection in November, this will be part of the historical record that will be used to assess his presidency. Vice President Biden's line about how the Obama presidency consists of "Bin Laden is dead and General Motors is alive" represents another element of how the President will be judged. Killing Osama Bin Laden and the bailouts of American banks and corporations will be something that the voters in their infinite wisdom will affirm or negate in terms of his election. I think that the recent discussion of gay marriage and the President having been the first sitting President to affirm the right of marriage extending to gay and lesbian couples will be another part of his legacy whose full judgement will have to be withheld until the results of the November election. History will judge President Obama in a more definitive manner with this result.