He got the peace prize for being the first black president, breaking an over two hundred year old taboo in a nation priding itself on its liberty, if not its history of slavery and violence. It was a coming to terms, a reckoning, and it was, and it is.
If we are talking about geopolitics, yeah no, you don't start with a fresh board when you become president. You're knee deep in shit that's been accumulating for a century, you have alliances, you have covert ops, you have wars, you have puppet dictators, you have vested economic interests as a matter of being responsible for the nation's continued existence- most of which was built on slavery, military power, subterfuge, assassinations, uncomfortable alliances, and a vast network of tentacles controlling global industrial infrastructures.
Yeah, you don't just get to say "we're not gonna do this anymore", because the USA is way in too deep at this point. There were literally military engagements going on at that point that you couldn't just withdraw from without creating way more chaos and destruction.
You have to see it from that perspective. It's disingenuous pointing at what is in the greater scope genuine details in how the USA has been waging foreign politics for the past century.
It was much better than what the Republicans had done if they had stayed in power. Obama did what he could with what he had and he did a shitload of good, but it's ridiculous suggesting there is any semblance of equivalence between him and the people who created the wars for profit that enriched the Bush dynasty and their cronies.