This movie is funny on a "This Is Spinal Tap" level, and better than just about all of Christopher Guest's numerous follow-up mockumentaries.
"American Movie" focuses mainly on Mark Borchardt, an independent filmmaker from Wisconsin and his permabaked friend Mike. Mark seems somewhat aware that the purpose of the film is to mock his backwater eccentricities, but still, he can only be himself for the cameras. The result is a hilarious, sometimes touching, unforgettable glimpse into this guy's little world and his giant dreams.
These same filmmakers (not Mark Borchardt) made another surprisingly interesting documentary called "Home Movies", about people and their unique, interesting personalities and houses. Also worth watching.