The big question about Obama is simply this: is he as good a president as Bush was bad?
Bush left the country two difficult to extract from occupations in Iraq and Afghanistan, a structural deficit that is the largest in history (meaning, even running at full employment, the government budget is structured to be in deficit), and cut long-term investments in infrastructure. He was the first president in history to start two major wars while cutting taxes. While I don't think that Bush is to blame for 9-11 or the worst financial disaster since the Great Depression, he obviously was unable to detect and stop these threats in time. Additionally, the man undermined progress on fighting climate change and attacked rights to privacy and due process. How bad was he? It would take any president years to undo the damage he'd done.
So now in order to be considered good, Obama has to reverse Bush's atrocious fiscal policies AND environmental policies AND extract American troops from two occupations. This just to get to zero.
Just to preempt his critics. yes, Obama did run for office fully aware of these challenges. JFK was quoted as saying that what most surprised him was that when he got into office he learned that things were, indeed, as bad as he had been saying while campaigning.
Obama can't just stand atop his own achievements at the bottom of the hole that Bush has dug. He has to be good enough to fill Bush's hole AND build something more atop that. Personally, I think that Obama is a good president. It is not yet obvious, though, that he's as good as Bush was bad.