I feel a lot of people exaggerate, are crazy tea partiers, bitter Occupy wall streeters (with fancy liberal arts degrees) and/or mostly hate him because he is half-black (aka racism!) This sounds crazy but let me explain. The time he came in is one the worst times in recent US history. After Bush (who was charming but who is a worst president than Obama). America was/is a mess. The war on terror was a bust (no weapons of mass destruction), our economy was rapidly/subtly failing (cuss of the mortgage crisis), and a lot of shifts were going on (lack of bipartisanship, tea party movements, etc. Boom the recession hit from 2007-2009. President Obama was elected a short time after. During this time a lot of things are going on. Bipartisan is very low (the dems and repubs just don't get along and won't get along). People are worried, they are losing jobs and can't get jobs. Auto industry failing (the infamous bail out), swine flu, a lot of transitions in America. President Obama was elected in a time of great change, and a lot of these problems existed way before he was elected. People blamed him, expected/expecting him to fix everything immediately.
Even so, the President has done a lot that people don't give credit for (it depends on the person and their political beliefs. (Legalization of pot, gay marriage (in certain states, finding Bin Laden, etc.) Some people claim Obama is a socialist (democrats are known for their left leaning social programs/support), a terrorist, don't believe he was born in America. Even after being given proof, a lot of people still believe in that. I can understand if you don't like someone based on their policies/beliefs, but demonizing them saying that he's un-American and not a citizen is just messed up. The logical step after this would be people are mad because he's black (mind you half-black, raised by white grandparents/mom). America still has very strong racial tensions (hello Trayvon Martin, Mike Brown, Eric Garner, etc.). This probably can relate back to times where African-americans were considered property and not citizens (or humans). By the way I feel some more negative opinions of Obama are fair. I don't think he is honest with the American public, he always flip flops/lies (says he will remove troops from middle east but sends troops for ISIS). I know this controversial but I don't care, had to say it!
If someone had to the worst president so far is perhaps Ulysses S. Grant 1869–1877. Idk history will tell.