Paul Krugman provides an interesting way of answering this question. In the first place, there is no point in asking that question to the legions of conservatives who have been taught to hate liberalism, and the president as the embodiment of that ideology. Bill Clinton got that treatment and Hillary will get it as well if she is nominated in 2016. We have a well funded anti-liberal, anti-progressive industry in America. Krugman is bothered, however, by the number of liberals, with whom he meets, who express their disappointments with the president. Many expected him to accomplish more than he has. Certainly, his rhetoric has exceeded his accomplishments.
Krugman proceeds to list the president's most significant accomplishments. Each of them is less than liberals might have hoped for, but they are significant nonetheless. Liberals would have liked Medicare for all, but we got ACA instead. Millions now have healthcare that they would not have otherwise been able to afford. Many would have liked more progress on climate change. Conservatives are livid about what the EPA is doing, and the coal industry is bitterly opposed to his policies. The rest of the world is getting the message that the US is more serious about limiting carbon emissions, and that we are ready to take a leadership position on that issue. Liberals would also have liked a more aggressive implementation of the Dodd-Frank banking reform bill. The Wall Street banks know more about what has been accomplished than the public. They have shifted their campaign funding away from the Democratic Party, and to their more reliable friends in GOP.
We may be victims of the "Great Man" myth. Many of us expect a president to wave a magic wand and change the world. Our democracy was not set up that way. Our system of checks and balances works the way it was supposed to work. Anyone who pays attention to the media in the US will also learn that it focuses more attention on the problems in the Administration than on its accomplishments which are less newsworthy than problems. Every Sunday, the TV news shows give Republicans an equal opportunity to tell their story to the public. They have made the attack on the US Embassy in Libya into an example of the Administration's failure for over two years. The president's foreign policy is constantly accused of being weak. We should not be surprised about this. It is a longstanding position of the GOP that all Democratic Administrations are weak on defense. The media, of course, are pleased to report whatever they are provided with by their friends in Washington who wish for a more powerful military response to every issue.
My bottom line is that we should not expect too much from any president. Moreover, we are much better off today than we would have been if we had elected any Republican to the presidency. The Republican Party bears no resemblance to what it was in the distant past. Dwight Eisenhower gave us the interstate highway system. He understood the important role that government could play in our economy. Since the coronation of Ronald Reagan the GOP has become the anti-government, and the anti-tax party. Its hard to think about anything that it would like government to accomplish outside of military aggrandizement.