The Economists provides a good review of Obama’s acceptance speech.
The Democratic convention:  Barack Obama’s pitch to the centre

PERHAPS because there are so few of them, campaign strategists for both Barack Obama and Mitt Romney can describe the undecided voters who will help determine the outcome of this year’s election with remarkable precision. On Thursday evening in Charlotte, North Carolina, on the last night of the Democratic convention, Mr Obama made his case for re-election directly to those elusive swing voters. Who are they? At Mr Romney’s campaign headquarters in Boston recently, senior aides told your correspondent that their target swing voter was a married, middle-class, middle-aged woman who voted for Mr Obama in 2008. Inspired by his promises and swept up in the excitement of electing America’s first black president, such voters now feel deeply disappointed by the president’s actual record, it was asserted. In Tampa last week, Republicans predicted that the president, unable to run on his record, would have to mount a negative campaign and seek to suppress Mr Romney’s vote, paving the way for a grim, ground-out victory on the backs of the various special-interest groups that make up the Democratic base.

Strikingly (and to his credit), the president made a more centrist, positive pitch in his acceptance speech. There were some clever swipes at the Republicans, but Mr Obama also touted his own record and told those who had backed him in 2008 that it was their record, too, seeking to anchor them in his camp. The disappointment question (all that hope and change) was deftly handled. The relationship between Mr Obama and his supporters had matured, you see, from a passionate affair to something more significant.

It was a risky approach that appears cold in print. Mr Obama told the crowd in Charlotte, “[T]imes have changed—and so have I. I’m no longer just a candidate. I’m the president.” But when delivered, the line was one of the most popular of the night. Staring deep into undecided America’s eyes, the president explained:

“So you see, the election four years ago wasn’t about me. It was about you. My fellow citizens—you were the change… If you turn away now—if you buy into the cynicism that the change we fought for isn’t possible…well, change will not happen.”
It takes some brass, as Bill Clinton would say, to run on a platform of change when you are the incumbent. But any incumbent holding office in times of gloom faces a double headache. First, they must argue that the current mess is not their fault. Second, they must explain why their clever ideas for fixing the mess have not yet been tried. On these counts, Mr Obama was only partly convincing.

The speech began horribly. Mr Obama launched what was, in effect, a synthetic proxy attack on globalisation. But after this leftish pandering the president tacked to the centre, and more or less stayed there for the rest of the speech. He talked of increasing energy exploration and extraction, especially of fracked natural gas, but also of subsidising renewable energy production and enforcing environmental rules covering things like offshore drilling. He vowed to preserve America’s military pre-eminence, while accusing Mr Romney of planning to increase defence spending beyond the levels sought by the service chiefs (it’s a bit more complicated than that, but it is true that Mr Romney’s defence spending plans are unserious). He denounced tax breaks for companies that send jobs overseas, but defended free trade.

The smartest bit of the speech dealt with the slightly cartoonish argument about the role of government that has dominated both party conventions over the past fortnight. The Republicans called government a menace that should simply “get out of the lives” of hard-working businessmen and ruggedly individual entrepreneurs. The Democrats, on the other hand, seemed to suggest that government benevolence was a more reliable protector of the rights of the little man than the profit motive. It is not either/or, Mr Obama argued. That this simple observation represented a marked raising of the rhetorical tone is a measure of how shrill the debate has become. His words amounted to a rebuke of angry partisans in both parties:

“We don’t think government can solve all our problems. But we don’t think that government is the source of all our problems—any more than are welfare recipients, or corporations, or unions, or immigrants, or gays, or any other group we’re told to blame for our troubles.”
The reception for all this in Charlotte was enthusiastic, even if Bill Clinton inspired more affection with his bravura performance on Wednesday night.

The magic of 2008 is gone forever. But Mr Obama, greyer and grimmer than he was four years ago, does not need magic to win re-election. In a sharply divided country in which perhaps 40% of voters on each side are camped in entrenched positions, he needs to keep up turnout on his own side, and hold onto enough centrists to make it across the victory line. Mr Obama’s convention speech was not the most exciting or convincing he has ever delivered. But it was not a bad pitch for the sort of winning coalition he will need.