I think a little historical perspective is in order. In 2008 the US was in a dark place. Eight years of Bush were winding up with two wars still raging, and imminent global economic collapse. People were losing their homes, losing their retirement plans, and sending their sons to war. The Bush administration characterized itself by campaigning with fear, and that become a weight around their neck: people were scared about the world. The world itself had grown wary of the US: how could the daddy of us all be so fallible, so mixed up that they invade nations without clear evidence of necessity; how could the greatest economy in the world make such terrible decisions that the whole system itself could be jeopardised?
Obama changed that. Obama showed the USA and the world that a black man could be President of a nation that would once have enslaved him. Obama showed the world that the American Dream, that American's can do anything they aspire to if they truly want it, was true. Overnight, the darkness in the US lifted, and the wariness of the watching world was turned to respect.
Has Obama made good on all his promises? Hell no, but what politician ever does? Is the US economy a failure? The recession may not be over, but the economy HAS grown - it IS in better shape than when Obama took the oath. Consider that the economies of the most of the world are struggling, and the US is a part of the world, whether they like it or not. The US is a part of the global economy, and not everything in the world is Obama's fault, nor does he have the ability to fix everything. The trouble with economics is that its only part science. The other part is human nature. Economics is about confidence, and the relentless browbeating of pundits that the economy is in a terrible state, that Obama is a failure, that business is strangled by Obama's Socialist agenda... its that nonsense that is helping subdue economic recovery, as much as anything else.
Healthcare reform was an election promise, and he did it, though watered down from what it could have been. DADT gone, as promised. Gitmo is, no doubt, one of those things he wanted to do but the technicalities and/or legalities are insurmountable.
Obama has said in his own words that he underestimated the politics of getting jobs done. Only a blind man would deny that Republicans have done their darndest to block him at EVERY step. Even the tiniest legislative decisions are labelled by his detractors as "nation destroying". Republicans have doubled the use of the filibuster compared to the previous admin.
So, in a global economy that is faltering around him, and in a political space where he is blocked and tackled at every turn, Obama has still got a lot of jobs done. Maybe not all the jobs he promised, but the odds are not in his favour. I believe Obama HAS brought positive change, even if we'd hoped for more. I believe he brought hope back to the US, and he certainly lifted the global perception of the US after 8 years of Bush.
Hope and Change? Maybe our expectations were too high, but we still got it.