Even though new rulers emerge, the entire system still works.
We don't elect people for life, there are sometimes shining moments that other forms of government never will ever see outside of a revolution and the biggest thing is the people are still in power - yes it is still true.
Take most of the other forms of governments, the people have less of a voice in any part of their history than we have right now. Like EU member countries who are having a serious issues with with the forced desegregation of people and limiting freedoms through uniformed laws across cultural lines. The EU member citizen doesn't have the rights we do, they can't control their government and it seems that even though they criticize us, our simple system seems to still work.