The film is primarily the narratives of many first responders, so they play a large roll in the meassage being protrayed. They are seen as heros but also paid the price of their decisions through health issues.
The film is geared towards the general public, all medical terms are explained fairly well. No medical or first response background is necessary, and it is fairly educational for viewers.
The real threats of air quality were covered up due to politics and other reasons, wanting to get america back to work. Instead, the reports were edited and people were sent back into the dirty air to clean up the scene or back to office jobs in the area, with contaminated air surrounding everything. Decontanimation efforts did not start until very late in the process. Bush did not wear a mask and the workers were told they didn't need to, so they didn't. As a result, there were severe health problems afterwards.