If he had been elected in 2008 (assuming he didn't start a nuclear world war ... not a good assumption there), there would be much more damage to the Second and First Amendment, we'd have McCainCare, and he'd be well on the way to 'nationalizing' most industries.
It is a reasonable speculation that McCain would've been worse for the country than Obama.
A McCain administration would've given the Democrats pretty much everything they wanted -- since the Republican Congressional minority couldn't have united in opposition, as they did to Obama.
Plus, we would've had the spectacle of a President who couldn't resist getting involved in every conflict around the globe. And with a Presidential temperament that would brook no dissent.
In the long run, we may have dodged a bullet. Certainly, the 2008 election presented the American public with a choice between the equivalent of Scylla and Charybdis.