The documentary that inspired this thread was the enigmatic and visually stunning Manufactured Landscapes
(2006). What makes it so scary is how beautiful it looks. Many scenes are beautiful if you don't know what you're looking at. Turn off the sound and your watching abstract landscapes with the florescent red rivers, etc.... However it documents the environmental disutopia that is the industrially developing world. When the narrator tells you what you're looking at ... sewrage and heavy metal polluted rivers and the remains of decades old coal mines, etc... then reality seeps into the real world.
More effective as a scientific and social morality tale then An Inconvenient Truth