Gandhi died before he was awarded the Peace Prize, even though he was nominated five times. Obama gets it less than a year into his Presidency? I like Obama, but that's just wrong.
Prior to Obama, some people in the international community had grown disenfranchised, resentful, bitter and distant with the US. I'd like to say it was a great number or a majority of people, but I don't have a study or link to back this up. This is just from my experience.
The accomplishment that Obama did, which for US citizens might seem inconsequential, is that they made us (the international community) look at the US with fondness. Changing people's mind is a powerful accomplishment.
Obama's administration made people have faith in US leadership and that once again the international community's voice would be heard by the lone reigning super power in the world.
This isn't a "concrete" accomplishment like publishing a paper, stopping a war or ending an oppressive regime. But it is nonetheless a relevant and important event in the course of international politics. By positively changing the political climate Obama has achieved something that the US had failed to do for many years.
Honestly, I don't understand all of the hate. Peace itself is an ideal, a goal we should aim for but most likely will never achieve (at least not on a global scale), and Obama's intentions and steps in that direction have spoken louder than many others this year.