NEW YORK (Reuters) - When Oscar-winning director Alex Gibney began filming the story of drug-addled U.S. journalist Hunter S. Thompson at the late author's funeral, he says it was one of his "greatest failures" in making the documentary.

"Nobody wanted to talk, so we just sat there with a camera crew ordering room service, it was pathetic," said Gibney, recalling the estimated $2 million dollar funeral in 2005 funded by actor Johnny Depp and attended by other celebrity friends such as actor Bill Murray.

"They felt this is Hunter, he is very personal to us," he said. "And they did not know me and thought, who is this guy?"

But with the eventual help of Depp and Vanity Fair editor Graydon Carter to gain access to Thompson's records, Gibney finished "Gonzo: The Life and Work of Dr. Hunter S. Thompson" that is released in the United States on Friday.

Thompson, famed for developing a first-person narrative "Gonzo" style of journalism that borrowed fictional techniques, as well as for frequently using hallucinogenic drugs, pills and alcohol, shot himself at the age of 67 at his Colorado home.

Early reviews have praised the film, which focuses more Thompson's writings and impact on modern journalism than his experiments with drugs.

"Gonzo has a wealth of delightful archival footage to draw on, both directly involving Thompson and evoking the cultural landscape around him," Variety said in its review.

POLITICAL IMPACT

The documentary examines Thompson's works, including his first piece for Rolling Stone magazine about the Hells Angels motorcycle club and his books "Fear and Loathing in Las Vegas " and "Fear and Loathing on the Campaign Trail."

Gibney uses interviews with colleagues and subjects including defeated presidential candidate George McGovern, who Thompson wrote about while covering the 1972 presidential race, as well as British illustrator and longtime collaborator Ralph Steadman.

"He (Thompson) found invasive ways to get at the truth, in ways that were more unpredictable," said Gibney, 54, who won last year's Academy Award for best documentary for his film "Taxi to the Dark Side."

Gibney said he was not an obsessive Thompson fan. But in the 1970s he read "Fear and Loathing in Las Vegas," which he felt precisely portrayed his own counterculture experiences.

"What I didn't see then was these larger grander themes about the character of America and the death of the American dream and all of that," he said.

Gibney's documentary includes footage from previous Thompson films including Bill Murray's "Where the Buffalo Roam" and the fictional 1998 film version of "Fear and Loathing in Las Vegas" which starred Depp, who narrates Gibney's film in a voice similar to Thompson's.

"He (Depp) feels very deeply about Hunter, there is something about how he and Hunter clicked," said Gibney, recalling how Depp spent time living with Thompson and studying him preparing for his role.

But ultimately the documentary is not another film about celebrities who knew him recalling wild stories about his drugs and drinking, but about his political impact.

"Everybody had forgotten about why they were interested in him to begin with," said Gibney. "What a great writer he was and particularly what a great political writer he was."

(editing by Alan Elsner)