The thing that I see most in Obama's presidency is that he has forced into being almost totally reactive on most issues. The economy was in dire straits when he took over and he was forced to deal with it... and in large part he was bound into the stimulus spending strategy that Bush's administration had embarked on. Afghanistan and Iraq, he was similarly bound to what his predecessor had started until there were was an opportunity to change the strategy. The spill in the Gulf of Mexico is similarly something that was largely out of his hands: about all he could have done would have been to step up inspections and safety protocols on those projects but its also a case that most people outside the industry don't realize there's an issue until something catastrophic happens. The biggest accomplishment of the Obama administration, in my mind, was the health care reform and it was a starting point, not a complete solution, in large part because he had to weaken it to mollify members of his own party.
As far as things like getting rid of the partisanship in Washington, he's trying but thats not something he can do alone. Too many Dems and Republicans have too much to gain by keeping the electorate polarized and divided, even if it isn't the best thing for the country.
On the whole I'd give him a C so far, which is quite an improvement from Bush but he's got a long way to go.