If Obama were working with the Congress in the 80s and 90s that didn't appear to want to kill each other, I'd give him a C-. He could have done a lot more and if this is all he had to show for it, it would be rather disappointing. However, working with what he has which is two sides that hate each other to the core, I give him a B-.
I think lots of people fail to remember their classes in American government. While 50 votes is all it takes to form a majority, it takes 60 to form a filibuster-proof super majority and avoid the minority party from taking the Senate hostage. So to say that the President could have passed anything he wanted in the first 2 years of his term is inaccurate.
I think history will judge him as being the anti-Bush who worked to correct all of the horribleness Bush gave us: 2 wars, massive deficits, worst depression since the 1930's, huge unpaid tax cuts, etc. At the very least, he appears to be calm, level headed, and appears to respect his opposition (the same could not honestly be said for the other side, which is downright hostile at this point). We'll see.
One other thing, at this point, I would take John McCain over Mitt Romney as president any day of the week. One person I respect, the other I do not. The amount of violent fervor on the right is like a dark demon that wants to spring loose. It cannot be tamed. John McCain purposefully fought against it (and lost). I'm afraid Romney would try to tap into it to win.