Let me be clear that when the Democratic primary season began in 2007, I was a supporter of Bill Richardson, a guy who had served with distinction at every level of American government. The guy is a genuine public servant. I never cared for Hillary as I saw her as an extreme corporatist like her husband, of whom I also was never much of a fan for the the same reason. That said, the GOP provided no alternatives that I could live with as the party had destroyed McCain Version 2000. The most serious legitimate critique of Barack Obama when he was a candidate in 2008 was that he lacked substantial experience in elective office, and what experience he did have was not especially noteworthy. It was hard to argue against those facts so I wasn't enthusiastic. But it eventually became clear that he would be the nominee so, reluctantly at first, I supported him, and then enthusiastically, after reading The Audacity of Hope. In that book, he showed me he had the historical background to understand where we've come from as a nation, how we got to where we are in many areas of public policy, where we had to go, and how to get there. In the absence of genuine experience, it's sometimes possible to acquire a form of experience from the right sort of learning and this was the best available. Regardless, no candidate is prepared for the Presidency so it's a matter of considering weaknesses that can be overcome, allowing strengths to come forward.
That said, Mitt Romney is the most inexperienced politician to run as a major party presidential nominee since Adlai Stevenson lost to Ike in 1952 (well I guess except for Ike himself who'd held no elective office at all. Of course, he wasn't exactly a run of the mill politician, having managed and won World War II and all.). Mitt was a one-term Republican governor in the most Democratic state in the nation where that office is very weak. The legislature really runs the show there. Besides that he worked at Bain as a corporate raider and redeveloper at the higher levels of the American business world. That's it. He was raised as a stereotypical son of a rich guy. George Romney came from not much to make something of himself and eventually ran AMC (creator of The Pacer automobile as well as my first car, the AMC Matador Station Wagon, 1973 for me) then became the Republican governor of Michigan (where the trees are the right height) with a stellar reputation as a genuinely compassionate moderate in an era when such politicians were in abundance. George might have had a good shot at the GOP presidential nomination in 1968 had he not been honest about why he changed his initial stance in favor of the US involvement in the Vietnam War ("I was brainwashed by the generals"). Honesty doesn't get you far in American politics.
Mitt has little of his father's experience and has shown no awareness of any other experience outside of that of exactly what he is: a rich guy who grew up as a rich kid. The business experience he claims is his main (sole?) qualification for office is very limited. High end and successful for sure, but limited. He might understand an oil company, but he doesn't know a thing about running a gas station.
So when applying the same standard from Obama '08 to Romney '12 (again, not normal in US politics), the critique is precisely the same, perhaps worse for Romney. He ain't got the chops.