Unlike John, I thought Obama's speech was thematically coherent, its basic message being: "Our ideals helped us do great things in the past. We took an unfortunate detour these last eight years. But now we're back."
There's very little in the speech that doesn't relate to this theme in one way or another. The direct shots at Bush obviously do ("[w]e will restore science to its rightful place," "a nation cannot prosper long when it favors only the prosperous," "we reject as false the choice between our safety and our ideals," etc.) As do the slightly more veiled criticisms of the last eight years. For example:
Time and again these men and women struggled and sacrificed and worked till their hands were raw so that we might live a better life. They saw America as bigger than the sum of our individual ambitions; greater than all the differences of birth or wealth or faction. ...
Our capacity remains undiminished. But our time of standing pat, of protecting narrow interests and putting off unpleasant decisions - that time has surely passed. Starting today, we must pick ourselves up, dust ourselves off, and begin again the work of remaking America.
You can immediately locate the speech's three key elements here: Storied history (all those sacrifices), tragic interregnum (those years of standing pat), reclamation of our destiny. I thought they were very effective.
To the extent the speech had problems with coherence, they weren't thematic but stylistic. One minute Obama was on top of Mount Olympus ("We remain a young nation, but in the words of Scripture, the time has come to set aside childish things..."), the next minute he was having lunch in the Brookings cafeteria ("Our health care is too costly ... We will build the roads and bridges, the electric grids ... it helps families find jobs at a decent wage ... We will begin to responsibly leave Iraq...") It was like two speeches on the same topic written for two different audiences on two different occasions.
John wanted Obama to tease out his arguments more. I'd have gone the other way--losing the specifics and the arguments and making the metaphors more vivid, the language more lyrical, and the tone more inspirational. All in all, I'd like to have seen something more along the lines of Obama's famous New Hampshire concession speech (especially the second half) than his more earth-bound convention speech. The first priority of an inaugural is to animate a presidency, not lay out its agenda. There are plenty of opportunities to do that down the road, not to mention the campaign we just had.
Why'd Obama do both? I'd guess the speech tried to preempt the same criticism that's been leveled at the inaugural festivies--that they're too lavish and precious for a time when people are hurting so badly. Obama seemed worried that soaring words without a nod to Americans' daily struggles would invite the aloofness charge he's faced before. Which is how we ended up with those rhetorical highs and lows. (For that matter, even the highs weren't as high as we're accustomed to--for the same reason, I suspect.)
Problem is, a single speech isn't like a week of inaugural festivities. You can hold lavish balls one day and service projects the next, and no one suffers for the dissonance. But an inaugural speech needs to hang together.
In any case, I agree with Michelle Cottle: The bleak circumstances make a full-throated celebration all the more important--people need a little uplift and escapism at a time like this, maybe a little something to aspire to. In the same way, down-and-out people are even more starved for lyricism and inspiration--at least when they tune into a symbolic event like an inaugural. Obama should have given it to them and saved the wonkery for his state of the union.
Update: I just watched Obama's speech on television for the first time. I'll stick with my original critique, but I have to concede that the lyrical spots were more lyrical than they seemed in person. One technical problem: Obama tends to play off crowds--he leans into them to generate his rhythm. But even though there was a massive crowd today, the noise was so dispersed that Obama didn't get the usual interaction.