Yeah, not so much.
1. The president is rusty or worn out. As Jake Tapper tells it (no link), this is the version of Obama from the summer of 2007, where the listless senator lazily moved from chore to rhetorical chore at the stump. He didn't prepare enough, didn't expect much from his opponent, and didn't think he needed to fight too hard when he's this far ahead.
2. Obama was thrown by Romney's new new positions. Matt Yglesias is right off the bat with the assertion that Romney has once again shaken the Etch-a-Sketch, this time redrawing himself as a reasonable moderate who knows that "regulation is essential" and that Medicare must be preserved by making "benefits high for those that are low-income". The latter policy is redistributionist in a way that is completely reasonable and popular. The former is at odds with the highly unpopular far right.
3. Strategy It's probably that this is giving the Obama campaign too much credit, but there could be something to say for playing prevent defense. If the campaign decided that it's better not to tip their strategy for the final two debates, they may have encouraged the Pres to hold back (I think this is a mistake). More, though, they could reason that since Obama is very far ahead in the polls (by modern standards), it's better to make no news. Something arguing in this hypothesis' favor is the fact that very few campaign surrogates showed up to the "spin room" afterward to tout Obama's performance.
If this latter hypothesis is true, then it was probably a blunder. Right now nearly all the networks are out talking about how Romney won the debate, and nothing seems to move public opinion like consensus opinion in the media. The polls will probably start to move toward Romney in the coming week, and it's not hard to see why: his sales pitch was much better and none of his lies was effectively countered.
Other thoughts:
Romney's argument over teacher employment was masterful. Obama correctly points out that more than 100,000 teachers have been fired since the beginning of the recession. Romney counters that Obama "put $90 billion into green jobs. ... that would have hired 2 million teachers." This is clever because it at once knocks the Pres for the Solyndra failure and implies that his priorities are all talk. It was entirely dishonest, because spending on teaching is in the "discretionary budget", which Romney wants to decimate, and because the green energy money was earmarked in the American Reinvestment and Recovery Act (AKA The Stimulus), and hence could not have been used for this purpose. However, this point went uncountered by Obama.
A discussion about the Independent Payment Advisory Board was drummed up by Mitt:
Number three, it puts in place an unelected board that's going to tell people, ultimately, what kind of treatments they can have. I don't like that idea.
Afterward, fossilized nitwit George Will (rated one of the worst political prognosticators) proclaimed that this will become a major issue in this campaign, virtually ensuring that it will not. Unlike some of the other points, the president argued against this head on, and I didn't get the impression that this "death panel" nonsense served as anything more than a Republican dog whistle.
All of this being said, debates have not historically made much difference in presidential races.
Voter intentions before (x-axis) and after (y-axis) debates. The line represents "no change". Source: Erikson and Wlezien via Wonkblog
The only exceptions one can point to are 1976 (when Gerald Ford stupidly said that Poland was not under USSR control) and maybe 1988 (when Michael Dukakis, with no emotion, denied that he'd want the death penalty if someone raped his wife). Debates happen late in elections, when most people have made up their minds.
Nonetheless, Obama didn't do himself any favors tonight.