I have a certain amount of experience with Americans. I also have family in California and Miami. In general the Americans I got to hang out with were regular, intelligent and sociable people.
For example I traveled with two Americans from Paris to Normandy and we did a tour of one of D-Day beaches and visited the allies cemetery together. I also traveled Edinburgh with some very cute American girls.
People like to say that Americans are ignorant, especially ignorant of the outside world. While unfortunately that is true to a certain extent, I also found other supposedly people from cultured places guilty of the same. The average Americans I hanged around with were smart and pretty easy going.
The bottom line is that each of us needs be a judge of character and decide on who is worth spending our time with, so spend time with cool people and avoid jerks no matter the nationality or culture.
In short, I've served with a few Americans in the army, excavated with American students and volunteers, traveled with Americans, etc. And they come in all shapes and sizes. Some are clueless as to environments outside their safe zone, others are curious and receptive, some are spoiled and self centered, others are experienced. To say that I find a certain underline mentality or spirit to all Americans I've encountered through the years would not be simple. Some became my best friends, some got on my nerves. While I find that I share many values with them, there are also cultural differences, but I don't think there is any factor or taboo that sets Americans apart for ridicule.
I find that when it comes to common people, at least in developed countries, most people are more or less the same.