Miss Knox and her ex-boyfriend Raffaele Sollecito were convicted and imprisoned for the 2007 murder of Miss Kercher, a 21-year-old student from Surrey.
Both spent four years in prison but were cleared of murder last year.
The LA Times said the film explores the case “with laser-like precision”.
“This strong documentary sheds a powerful light on this particular case while emphasising the ultimate unknowability of absolute truth.”
Miss Knox has been interviewed at length for the documentary, which was released on Friday.
The film also features interviews with Mr Sollecito and Italian prosecutor Giuliano Mignini.
Writing in The New York Times, Jeanette Catsoulis described the documentary as a “tightly edited, coherently structured and ultimately moving reassessment that burrows beneath the lurid in search of the illuminating”.
But The Guardian described the film as “intriguing but flawed”.
“This film could have looked harder at the authorities’ murky and compromised mindset, and made that the focus of their film,” Peter Bradshaw wrote.
“Instead, they do a steady job of interviewing most of the main players, keeping a deadpan if spurious air of mystery, as Knox says some faintly melodramatic stuff about being perceived as a “psychopath in sheep’s clothing”.
The Wall Street Journal said the movie “makes a virtually airtight argument for [Knox’s] innocence”.
“While Amanda Knox would seem to continue the exploitation of its subject, Ms Knox herself is involved so, one presumes, the payoff is guilt-free viewing. The bonus: some clues to why the now-29-year-old University of Washington grad became a tabloid villainess in the first place.”
Miss Knox herself said she is not a “terrible monster” ahead of the release of the documentary.
She said she wanted to be involved in the film to show the “nightmare” she had been through.
“I think I’m trying to explain what it feels like to be wrongfully convicted,” she told Good Morning America.
“To either be this terrible monster or to be this regular person who is vulnerable.”
After appeals and retrials they were acquitted last year by Italy’s highest court.
“What I’m trying to convey is that a regular person like me – just a kid who was studying abroad, who loves languages – could be caught up in this nightmare where they’re portrayed as something that they’re not,” she said.
“There remains the fact that I’m in a unique position as an exoneree. Once an exoneree always an exoneree. I can’t go back to my life that I had before, and neither can the other exonerees that are out there.”
Miss Knox, who has said she was not paid to be involved in the documentary, said the prosecutor’s focus on her meant Miss Kercher had been “lost” in the case.
She said: “For [the Kercher’s family] that’s never going to end and that’s the really sad part about this tragedy.
“As soon as the prosecutor made this about ‘it has to be Amanda, it has to be Amanda’, they took away the fact this case is about her.
“She’s been lost in all of that. But that doesn’t change the fact that we have also an obligation to everyone who could potentially be innocent to find out the truth for the sake of the victim, and for the sake of them as well.”
On Thursday evening, Mr Sollecito told BBC Newsnight that he needed to rebuild his image before he could rebuild his life.
He said: “People never understood the truth about this case. They never knew about us.
“The victim is Meredith Kercher, but there are other two victims who are alive.”
Mr Sollecito said it was “ridiculous” to suggest he was protecting Miss Knox out of a sense of loyalty, given the couple had only been together for a few days when Miss Kercher was killed.
“After five days, I didn’t know her, so why should I be loyal to her,” he said.
He said he and Miss Knox now have “a good relationship”, adding: “We don’t talk too much because we are very distant, and we are caring about our lives.”
Mr Sollecito is now seeking compensation for his legal fees, which he says have cost his family more than $1m (£771,000).