My instant reaction to the debate: I'm kind of amazed at how well Obama did. Granted, I'm an Obama supporter and a pessimist, so I guess I went into the debate with low expectations. Still:

I think Obama succeeded in striking a very delicate balance: He had to be sharp and feisty and tough (to erase those particular doubts about his first performance), but he had to stop short of Joe Biden levels of aggressiveness and remain essentially likeable. I think he did that. I've heard some commentators say Obama was "angry," but he didn't strike me as crossing that line -- except maybe a few times when he displayed righteous indignation that I thought was effective. Certainly he didn't seem angrier than Romney, and he wasn't as disrespectful of moderator Candy Crowley as Romney was.

Obama also handled several specific challenges well: