Philip Klein's take:
Pawlenty has a compelling personal life story and has been can be perfectly likable in person. Were he to have simply been himself, he would have had a better chance to bond with voters on a personal level. And if you do that, they're more forgiving when you explain various "clunkers" in your record, as Pawlenty liked to put it. Unfortunately, Pawlenty's need to make up for his various deviations from conservatism resulted in a consultant-driven, overly scripted campaign. That's the exact opposite of what he needed to do if he was going to differentiate himself. Nobody is going to out robot Mitt Romney.
[D]espite some blue-collar posturing, [Pawlenty didn't] run on anything remotely like the kind of "Sam’s Club" conservatism that he once seemed poised to champion.
Some of the time, as Matt Bai writes, he seemed "tentative and risk-averse," trying to be all things to all conservatives instead of forging a distinctive identity of his own. Then when he did stake out strong positions, he cast himself as the supply-sider’s supply-sider and the hawk’s hawk, promising magical growth unicorns and interventionism without end. It was a peculiar strategy: He was trying to fill the populist space that Mike Huckabee had left vacant, but he spent most of his time either imitating Mitt Romney’s unsuccessful “Mr. Conservative” campaign from 2008 or else channeling the policy preferences of the Wall Street Journal editorial page.
Calling Pawlenty "the canary in the establishment coal mine," James Poulos argues that his status quo message "no longer computes with a critical mass of Republican voters: not just in Ames, Iowa, but nationwide." Earlier eulogies here.
(Photo of a card handed out by the Pawlenty campaign at a town hall in Boone, Iowa last week. By Weigel)