Jason Buchanan of All Movie Guide says of it :
Enron: The Smartest Guys in the Room director Alex Gibney turns his attentions from corporate scandal to Gonzo journalism with this tribute to the libido-driven, Wild Turkey-swilling writer who never knew the meaning of the word "excess." Comprised largely of never-before-seen archival materials, Gibney's film focuses on the years between 1965 and 1975, when Thompson was truly firing on all cylinders. Rare home movies, audiotapes, and excerpts from unpublished manuscripts combine to paint an affectionate portrait to the wild-eyed father of Gonzo journalism.James Rocchi reviews it at Cinematical, and David Carr in The New York Times. The astonishingly tasty Johnny Depp (who you will remember financed Thompson's very appropriate funeral) reads the author's words, and many other famous political figures and authors are interviewed.
Here's the trailer and if that's not enough, more snippets can be found here :
(Picture at top taken from Cinematical.)