The trouble with that is when the choice you have is "which is the lesser of two evils?".
How would an American vote in Europe? Our mainstream right-wing parties are to the LEFT of the Democrats!
Or to take a real-life example - me. When I went to vote in my last parliamentary election, I didn't even have a candidate available to me in my party of choice!
Okay, we do have the option of standing ourselves, it's not that expensive, but I have TWO characteristics for me, that would demonstrate how "democratic" an election is. One characteristic of a good system is "how many people are represented by the candidate they voted for". That is a GOOD metric (but easily subverted by a dictatorship - just have one candidate per election!). The second metric is "how many candidates stand a REAL chance of being elected". Not sure how to measure that, but in the UK for most constituencies that figure is pretty close to ONE. Not that much different from a dictatorship, really ... The US probably isn't much different.