But his supporters already know he can deliver powerful rhetoric. He wasn't trying to win over the crowd - after all, he'd already got them to fill a stadium.
No, this was a speech for the woman in a Frank Luntz focus group last week who said she was tired of rhetoric and wanted to hear some substance from the Illinois senator.
So he gave us his tax policy and his healthcare policy and his energy policy. With details.
Like a 10-year target for energy independence and the promise to make available to all the health plan that congressmen currently enjoy.
None of it would have surprised those who have studied the policies on his website, but this was Mr Obama's chance to explain his positions to a primetime audience and he grabbed it with both hands.
So - a substantive ending to a week of contrasts. We've had intrigue, feuds, reconciliation, showmanship and the odd policy thrown into the mix as well.
Join us next week from the Republican convention in St Paul for another helping.
MAX DEVESON: OBAMA'S BIG WARM-UP
28 August: 1930 local time (0130 GMT)
Al Gore got a big reception here at the Invesco Stadium - his narrow loss (depending on how you look at it) of the 2000 election and his subsequent re-emergence as an environmental Cassandra have made him something of a party mascot.
His speech tonight was rather lacklustre, however, especially in light of the appearance from New Mexico Governor Bill Richardson that preceded it.
Mr Richardson's speech was a non-stop series of jibes at John McCain, including the best zinger of the convention so far: "John McCain may pay hundreds of dollars for his shoes, but we'll all be paying for his flip-flops."
And he was the first speaker I have heard in Denver to explicitly accuse Mr McCain of "changing his mind on torture" - a reference to his support for a bill which did not explicitly ban the CIA from using controversial interrogation techniques like waterboarding.
By contrast, Mr Gore showed little anger, although he did offer one joke.
Accusing Mr McCain of offering the same policies as President Bush, he said: "Hey, I believe in recycling, but that's ridiculous."
One dud speech will do little to dent Mr Gore's popularity with Democrats. Besides, the speech that everyone's waiting for is coming at the end of the night...
JENNIFER COPESTAKE: DEMOCRATS GET DOWN
28 August: 1800 local time (0000 GMT)
Tonight, 75,000 people are going to pour out of Invesco Field and on to the streets of Denver to take part in what many people have told me is the most important part of the convention - and what they really came here for.
It's party time. There have been hundreds of parties here in Denver this week. Last night I went to the so-called "hottest ticket" of the night, Unconventional. I watched as Democrats young and older bust a move.
Delegates let their hair down at a convention party
MAX DEVESON: WHAT OBAMA NEEDS TO DO
28 August: 1530 local time (2130 GMT)
I'm sitting amid a forest of cameras and anxious producers on the field of the Invesco Stadium, as the 75,000 seats round me begin to fill up. It's hot and you're only allowed a sunshade if you're a camera.
As people begin to take their seats, and a local bluegrass band warms up the crowd (makes a pleasant change from the U2 and Bruce Springsteen songs on continuous loop being played the rest of the time), I thought it would be a good idea to sketch out what Barack Obama needs to do this evening.
His own campaign manager, David Plouffe, told reporters that Mr Obama will have succeeded if he explains "where he comes from, who he's going to fight for, what his change means, and the contrast with John McCain".
Separately, Mr Obama's chief strategist David Axelrod has said that the speech will be about "the risks of continuing down the road we're on, which is plainly what Senator McCain is offering, and he's going to talk about an alternative path".
Will this strategy please the Democrats who have been grumbling throughout the convention that the party has been unwilling to attack Mr McCain hard enough?
Joe Biden and Bill Clinton went some way towards taking the fight to Mr McCain last night, as did the grassroots hit of the convention, Montana Governor Brian Schweitzer on Tuesday night.
It will be tough for Mr Obama to rough up John McCain tonight without sacrificing his core message of change and hope.
But he may need to don boxing gloves rather than kid gloves tonight if he wants to wrest control of the political narrative away from the Republicans, who have been successfully managing to define Mr Obama as an inexperienced dilettante in recent weeks.
CONNIE BORDE: ON TO INVESCO
28 August: 1300 local time (1900 GMT)
Last day: we're getting our instructions about how to get into Invesco, the sports stadium where Barack Obama will be delivering his acceptance speech later in the day.
The logistics are mind-boggling, the list of do's and don'ts perplexing. Imagine getting 75,000 security-cleared people into a stadium. Luckily the weather forecast is good because we'll be sitting outdoors - waiting - for many hours. Our chairwoman, Christine Marques says: "Bring a book."
I look around the room at my delegation and my heart softens a bit. We've been in close quarters for the past five days. It's over soon.
Democrats Abroad. Our delegation is unique. We are fluent in 12 languages and we made a 125,000-mile journey from every corner of the world to cast our half-votes.
We are united and working hard to elect a Democrat to the White House this fall by getting out the vote from abroad. It used to be complicated to register to vote and we've made it easy.
When I watched the performance of our Democratic Party last night, I got chills. And most important, I realised that this is what makes all this work that we all do on a volunteer basis worth the effort.
On to Invesco, I'll report back later.
READERS' QUESTIONS ANSWERED
What is the mood of the Denver locals? Are they excited and enthused by Barack Obama? If so, do you think Colorado will go blue in November?Tim McSweeney, Dunedun, New Zealand
Jennifer: Most of the Denver locals I've met support Barack Obama but I'm not sure the feeling is the same in other parts of the state. At the hotel where I'm staying, just outside Denver, I've met some very passionate John McCain supporters and I've been told support for him is strong in many parts of Colorado. I think the race will be very close here.
Why don't the delegates get a vote on the vice-presidential nominee?Liza, Seattle, US
Max: Officially, they do get a vote. Joe Biden's nomination was put to the vote on the floor of the convention. But because he was the only nominee he was unanimously approved: all of the delegates shouted "Aye" when the question was put. Theoretically, however, they could have shouted "No".
Why have some Hillary supporters announced they will not vote for Obama? Kwaku Kurankye Kwatei, Hamburg, Germany
Why are these Clinton supporters getting so much coverage? Colin, Leeds, UK
Max: Some Hillary supporters were so passionate about their own favoured candidate - and less than enthusiastic about Mr Obama - that they decided to make a point of sticking with Mrs Clinton, even after she dropped out of the race.
They are getting a lot of coverage because divisions within political parties are always big news - divided parties tend to lose elections. They are therefore a valid story for journalists to cover. Sometimes journalists can be accused of seeking out disunity where there is none - but not in this case. Mrs Clinton won 18m votes in the Democratic primaries, and polls suggest that as many as 27% of her supporters are unwilling to back Mr Obama.
The delegates were almost evenly divided, after the primaries, between Barack Obama and Hillary Clinton. What obligation is there (if any) to vote for Barack Obama? Can they still vote for Hillary Clinton? What influences how a delegate votes?Ed Corbett, Bridgend, UK
Connie: Under the rules, pledged delegates (delegates elected in the primary) are obligated to vote for the candidate they are pledged to - on the first ballot. If the candidate releases his/her delegates, those delegates are then free to vote for the other candidate - or not.
Max: In fact, Hillary Clinton did release her delegates before the first ballot. Many of the delegates she had won in the primaries chose to switch their vote to Obama. Then, in a theatrical moment, when the roll-call of states reached New York, Hilary Clinton dramatically moved to end the roll-call vote and called on the delegates to approve Barack Obama's nomination by acclamation. The motion was passed, and Mr Obama became the party's official nominee.
Connie Borde is a super-delegate representing Democrats Abroad. She has lived in France for some 40 years, and lectured for half of this period at the prestigious Sciences Po institute in Paris. She has authored or co-authored books on American cooking, American politics, and English grammar - and is currently translating Simone de Beauvoir's The Second Sex. "I always supported Barack Obama," she says. "But I waited to give my super-delegate vote until February 2008 when Democrats Abroad France (my constituency) voted in his favour by 71%." She has a French husband, and six children.
Max Deveson, 30, is the BBC News website's Washington reporter. He joined the BBC in 2001 to work as a political analyst in Westminster, later moving to the online world news team. He has an obsessive interest in the US and its politics and was particularly excited to land an interview with Ted Kennedy on his first assignment in Washington this year. When not obsessing about US politics, Max enjoys attempting to play Iron and Wine songs on the guitar.
Jennifer Copestake, 25, is an online video producer for World News America. She's been with the programme since its first broadcast in October 2007. After the conventions she'll be video-blogging from a BBC election bus on a 38-day road trip across the country. Jennifer was born in Canada and has reported for the CBC, the Hill Times, the Observer and More 4 News. She's been in Washington since early summer, but will return one day to London, where she lives with her fiance and two cats.
The BBC News website will also publish a diary of the Republican Convention, featuring Louisiana delegate Mike Bayham.
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