Over at PostPartisan, I'm arguing today that Romney is underrated, and actually has important political skills. I don't think it's just luck that he's emerged as the almost-certain nominee.
Projecting that forward...here's what I expect. Romney will be under a lot of pressure, just as John McCain and George H.W. Bush and Bob Dole were, to find a suitably conservative running mate to excite the party. He'll handle it reasonably well, more like Dole than like the other two. He'll give a solid convention speech that will beat expectations...that's an easy one, all the mediocre orators and nominees who have struggled during nomination season beat expectations in their convention speeches. He'll perform adequately in the presidential debates...no way to predict whether he'll "win" them or not, but he won't embarrass himself or his party. His campaign operation will be reasonably scandal-free, at least unless he's really heading for a blowout loss (for reasons other than his electioneering skills). His move to the center will be somewhat awkward, but that's more a function of the situation (and the current GOP) than the candidate.
In short, he'll be a perfectly adequate candidate. If he loses -- and Obama is probably a slight favorite now, but if the economy really is improving then Obama becomes a solid favorite -- he'll be seen as dull and uninspiring, and every campaign gaffe will be magnified in retrospect. Republicans will vilify him as not sufficiently conservative to have excited the party. But in reality, every candidate commits gaffes, every candidate has weaknesses to attack and exploit, and every candidate is insufficiently conservative for the current GOP.
Of course, if he wins, people will discover no end of virtues in him, and a lot of those will be overblown, too. He's not a great politician. But he's a good one, and he'll almost certainly be an adequate general election candidate. Which is, really, the best a party can hope for most of the time.