Here’s what those viewers missed:

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Outside the hall

Not everyone was a fan of what was happening on the University of Denver campus.

About 150 protesters with Occupy Denver marched down Yale Avenue, some eight blocks from the campus. Protesters shouted slogans denouncing a two-party system and the war in Afghanistan and demanding affordable health care.

Jason Leher, a 23-year-old Evergreen State College student from Denver, was cutting out paper letters for a large blue sign that read, “The whole world is our free speech zone.”

Others carried signs reading, “Both parties suck.” Others read, “Demand real debates.”

Just before the debate, police diverted the marchers away from the campus.

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Quiet, please

Some of the debates leading up to Romney’s nomination were a bit on the boisterous side, to understate it.

Applause, hollers and boos punctuated some of the GOP primary debates, with now-vanquished contenders Herman Cain and Newt Gingrich playing more to the audience in the hall than the one watching at home.

Not this time.

Repeatedly, before the candidates entered the hall, organizers chided the audience of 975 — a third each from the Obama campaign, Romney campaign and organizers’ picks — to behave.

If they didn’t, moderator Jim Lehrer warned, he would ask Michelle Obama and Ann Romney to help enforce the rule against audience reaction to answers.

The audience sat shrouded in darkness throughout the debate. And they largely followed the guidance of debate officials, interjecting laughter only twice — once when Obama mentioned his 20th wedding anniversary to Michelle and again near the end of the debate when the president mentioned that it would be hard for Romney to work with Democrats at the same time he was repealing the health care law they helped pass.

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The physical moves

When Romney all but accused Obama of lying about his tax plan, the president alternated between looking directly at his Republican rival and bowing his head to take notes.

At another time, Romney looked to the moderator, waving his hand slightly in the air to indicate that he wanted to jump into the debate. He then insisted that he wanted to have “the last word.”

To be sure, a lot of the exchanges will not be reflected in the transcript.

The president spent much of his time at the podium bowing his head and taking notes, or staring directly at his opponent. He balanced his weight on one foot, crossing his right leg behind his left foot. At one point, a loud thud could be heard coming from backstage. Obama took notice, turning around briefly, though nothing was visible from the stage.

At other times, Romney alternated between a forced smile and surprised scowl as the president spoke.

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The end

After the pair finished their 90 minutes of sparring, each walked across the stage to shake hands.

“Good job,” the president told his challenger.

Soon after, Ann Romney walked up the stairs, making an excited and triumphant gesture toward her husband before embracing him. Following her up on stage? Four of Romney’s five sons, one of his daughters-in-law and two of his middle school-age grandchildren.

The Obamas both shook hands or chatted briefly with the Romney clan, with Obama at one point bending down to introduce himself to Romney’s granddaughter Chloe.

The president departed the arena within minutes of the debate ending. There was a sharp chill in the air, a drastic shift from the warm and sunny weather that greeted Obama upon his arrival earlier in the day.

Romney lingered on stage longer than the president. He was holding his notes in his hand, the paper folded vertically; he tapped his son Josh on the lapel with the paper and handed it to him. Josh tucked the notes into his suit jacket pocket.

Right before he walked off stage — the president already gone — Romney turned to the audience and put his hand over his heart and waved, a wide grin on his face.

Many whooped and cheered.

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Twitter reponse

Romney’s sons took to Twitter to celebrate their father’s performance. “Now that was fun,” wrote Tagg Romney, the eldest.

Tagg then retweeted his brother, Josh.

“Clear eyes, full hearts, can’t lose,” Josh wrote.

The phrase comes from the TV series “Friday Night Lights.” A picture attached to Josh’s tweet showed Mitt and Ann Romney underneath a sign with that phrase printed on it and overlaid on the “R” Romney logo.

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The pregame

Romney spent much of debate day surrounded by his family. In the morning, he took time to meet with top advisers to finish debate preparation. But after he returned from a visit to the debate hall in the afternoon, four of his five sons joined him in his hotel room, along with wife Ann and two of his grandchildren.

He and Ann had a takeout dinner from The Cheesecake Factory — he had spaghetti and a barbecue sandwich.

Even before the debate began, the Romneys huddled together as a family. Mitt and Ann Romney watched their sons play Jenga, a game of stacked wooden pieces where players pull them out one at a time until the wooden tower falls.

Sons Craig and Matt Romney were shown in photos playing with Nick, who is Matt’s son and Mitt’s grandson.

Also before the debate, Obama got a visit from his wife, Michelle, who arrived in Denver on Wednesday afternoon following a solo campaign swing. The two rode to the debate together in the president’s black armored limousine, eliciting cheers from a crowd gathered outside Obama’s hotel on the first couple’s 20th wedding anniversary.