I don't agree with Dan Weintraub that often, but I think that he's nailed it here:

Way ahead in the early polls, Riordan expected a coronation but found himself in an election instead. He ran as a leader and a competent manager. But given the way he managed his own campaign, or failed to, it's probably best that he'll never get the chance to run the state.

The thing to remember about Riordan is that he was defeated for the same reason that Liddy Dole and John McCain were SOL for the Presidential primaries: if you want to get the Republican nomination for ANYTHING, it really helps if you're not a Democrat.