The movie takes its name -- not to mention its musical lietmotifs -- from the 1992 R.E.M. song "Man on the Moon." The title refers to various conspiracy theories about the lunar landing as an oblique way to comment on conspiracy theories about Kaufman's death in 1984. Because of Kaufman's love of hoaxes and disguises, many believed that he faked his own death as yet another stunt. In an odd way, Kaufman's Hoaxy side put him in a proud American tradition dating all the way back to Edgar Allan Poe, another Hoaxy fellow whose early death seemed (and still seems) like a hoax to many.
At the very least, Carrey deserved an Academy Award nomination for Best Actor. Looking back at the 1999 Oscars, I find it hard to view Kevin Spacey's Best Actor-winning turn in American Beauty as anything other than ridiculous. It's not just that this is fine work from Carrey -- it's also tremendously funny work. The Academy may undervalue comedy, but in acting, comedy is the hardest thing to do.
Danny De Vito and Paul Giamatti are also great as Kaufman's agent and head writer, respectively. The movie plays a bit fast and loose with the order of events to create a more standard Hollywood narrative. However, the movie also mocks this rewriting of history in Carrey's opening monologue. So there is that. Milos Forman and the writers keep everything both brisk and information-packed. This is a surprisingly informative biopic. Certainly we get a much better grasp of Kaufman's life and work than we did of, say, Stephen Hawking's in The Theory of Everything.
There's also a refreshing bit near the end that debunks New Agey mystical cures for diseases such as cancer, capping this film with a moment in which a dying Kaufman laughs at accidentally seeing behind the curtain of another performer's hoax. Highly recommended.