John McCain had a very strong start in the first 30 minutes or so, and I thought that he was heading toward a debate victory - his first. But he veered off course in the middle as the conversation turned toward the negative quality of the campaign - and he became more and more the angry, older candidate, bringing back memories of the performance by Bob Dole back in 1996 that helped to doom his campaign. He also seemed to grow more tired over the course of the debate.
Barack Obama had a good first answer about his economic plan then seemed flat for the rest of the first half hour. But then things picked up for him. During the assaults by McCain, he kept his cool - he never took the bait (rumors were heavy before the debate that McCain would try to goad him into losing his steadiness). Coming out of that second half hour, Obama became much stronger in the last third of the debate, scoring extremely well on health care, education, abortion, and the Supreme Court.
McCain likely helped himself with his base tonight, but I doubt that he helped himself much with undecided voters.
Overall, I would score Obama at an A minus for the night, and McCain at a B plus.
It appears that Obama will come out of these debates with a general public perception that he has won three in a row.
PS: A hearty salute to tonight's moderator, Bob Schieffer, he deserves an A plus.