He said he was still eager to reach an agreement on deficit reduction with Republicans but won't go along with more tax cuts for the wealthy. Nor would he go along with any plan to turn Medicare into a voucher program or to turn Social Security over to Wall Street.
Obama warned that much of what he has accomplished could disappear if he is defeated, but he said he hasn't given up hope.
"I have never been more hopeful about America. Not because I think I have all the answers. Not because I'm naive about the magnitude of our challenges," he said. "I'm hopeful because of you."
Immediately after the speech, Republican National Committee Chairman Reince Priebus released a memo titled "We Can Do Better."
"In 2008, Barack Obama had no record. His campaign was based solely on words," Priebus wrote. "This time, words won't suffice. There's a clear record, and it's clear we can do better. 'Incomplete' is inadequate," he said.
Romney campaign manager Matt Rhoades said after the speech that the choice in November would be clear for voters.
"Americans will hold President Obama accountable for his record - they know they're not better off and that it's time to change direction," Rhoades said in a statement.
The GOP also ripped Obama's promises as recycled ones that he's already failed to deliver on.
Earlier Thursday, Vice President Joseph Biden delivered a long-winded testimony to the president's character in his speech.
"This man has courage in his soul, compassion in his heart and a spine of steel," Biden said.
On the final night here, Biden fully embraced his role as party attack dog, describing in detail two conflicts the president confronted in his first term.
"Because of all the actions he took, because of the calls he made and because of the grit and determination of American workers, and the unparalleled bravery of our special forces, we can now proudly say - Osama bin Laden is dead, and General Motors is alive," Biden said.
Throughout the last night of the convention, Democratic officials paraded across to the podium to deliver their tailored critiques of Romney. Sen. John Kerry (Mass.) assailed the Republican presidential nominee from his home state for his lack of foreign policy, giving one of the most energetic and blistering critiques of Romney so far.
In another unexpectedly strong performance, former Michigan Gov. Jennifer Granholm roused the crowd with her defense of the auto industry. In a speech filled with fist-pumping and leg-kicking, Granholm struck a populist tone in her depiction of a GOP nominee who does not understand middle-class plight.
"In Mitt Romney's world, the cars get the elevator and the workers get the shaft," she said, in what may have been the line of the night.