What is a documentary film? Well, essentially it is a film that is supposed to document reality. There is a wide variety of documentary films. There are hundreds of historical documentaries, and there have been some very popular political documentaries as of late. Although in my personal opinion you will find many of the late political documentaries have a bias agenda.
For example, Al Gore released an extremely popular documentaries called "An Inconvenient Truth" which was about global warming. While many still say that global warming is not absolute truth and that we are merely in a cycle of a small change in the worlds climate, this documentary states it as thought it is a fact rather than a theory. It provides only the evidence that supports the theory. While the documentary is rather interesting, it obviously has a very bias agenda.
Other popular political documentaries are Michael Moore's films, "Fahrenheit 9/11" and "Sicko". Fahrenheit 9/11 was probably one of the most controversial films of the last decade. It contains outlandish comments about the Bush administration and even referring to the media as "cheerleaders" for the 2003 invasion of Iraq. Many people supported it, but those that disliked it found it necessary to make a rebuttal documentary of their own entitled "FahrenHYPE 9/11". The documentary is devoted to try to prove many statements that were made in the Fahrenheit 9/11 documentary as false.
Sicko made its own wave of controversy. It made comments about how poor the American government's healthcare system really was. I do not believe it made as much of an impact simply because most people are aware that our quality of healthcare is much better than most other countries, it is just the cost that is killing everyone. Michael Moore takes it to another level stating that even some third world countries have better healthcare. I think most everyone knows this is simply untrue. You can simply take a look at the rampant diseases in those areas to determine the truth on the matter.