You mentioned what Democrats don't like about the Democratic Party. Can you explain what Republicans don't like about (or would like from) the Republican Party?
There's a large faction of the Republican party that has become totally disillusioned with their imperialistic foreign policy, ridiculous bailouts and the skyrocketing deficits. They are typically marginalized as hypocrites, because "they didn't have a problem with it when Bush was doing it." But some of them did and have been completely ignored. These are typically fiscal libertarians and constitutionalists. Many of them choose to vote Libertarian or Constitution Party - or don't vote at all. But mostly they are disillusioned former Republican voters.
Remember that the turnout rate for voters is at unbelievably low levels. And Obama showed what can happen if even a small portion of that can be mobilized. Most Americans I talk to - typically more cultured ones that travel - understand that there is very little difference between the two parties. If a 3rd party came to the fore with a platform that appealed to both the anti-military adventurist, anti-bailout Democrats and
the civil libertarian/small government constitutionalist Republicans, I would not be surprised to see that "apathy/disillusioned vote" make a huge impact down the road.
But ballot access is the key. In many states, it is a 10 year process to even get on the ballot.