"did voters really believe the country was going to quickly and dramatically reverse course once he was elected?"
A lot of the time that's exactly what they did. I've often heard that people are disappointed in Obama because they expected him to wave a magic wand and fix everything. One woman said she voted for him because she thought he knew things others didn't, could do things others couldn't. if you're that dumb you deserve to be disappointed, but he rode that wave to get elected. The problem comes in trying to win re-election. I dread the idea of "Caribou Barbie" Palin ever speaking again, never mind winning the Presidency. Or someone equally demented.
I've thought about this a bit, as I do. Why do I want Obama to win? Is it coz he's black? No, it's because he's a Democrat. I always want the Democrats to win and the Republican to loose. Once in a while there will be a Rep who is just better than the Dem but my own dogma makes me lean left. That means I hope the Dems always put up good candidates.
So yeah, if you expect too much you will be disappointed, but let's hope the left gets itself together and rides on to victory in future, taking on board the lessons of this defeat.