The use of controversial video tapes in Diana: In Her Own Words has already been strongly criticised by royal watchers, and Rosa Monckton, one of Diana's closest friends, said it was a "betrayal of her privacy".
But Channel 4 said it gave the Princess a voice and placed it "front and centre" in the run-up to the 20th anniversary of her death in a car crash in Paris on August 31 1997.
The documentary featured Diana speaking candidly and informally about her upbringing, her courtship with the Prince of Wales, her troubled marriage and her public life.
Kensington Palace, the royal household of Diana's sons, the Duke of Cambridge and Prince Harry, has declined to comment on the documentary.
Writing in the Daily Mail, Jan Moir said she thinks Diana would have approved of the tapes being aired and that they show her in a "golden light".
She wrote: "Actually, I think that Diana would love these videotaped sessions from 1992 being broadcast. Adore it! For the recordings show her in a golden light; rueful, amused, heartbreakingly vivacious and beautiful, noble in her obvious loneliness.
"Here she is, scalded but brave, brushing up her oratorical skills as she prepares to embark on a new and independent life following her split from Prince Charles. The fabulous nerve of the woman!"
Moir added: "Much of this might seem like tired old ground, but the approaching anniversary of Diana's death and the haunting candour of her former aides bring a fresh intensity to her story.
"And there is something heartbreaking all over again in seeing those familiar images; especially that footage of a beautiful girl in a golden carriage, riding off to her doom."
However, Moir is critical of the "cheesy voiceover in full Old Testament mode", and says the tone was "often ridiculous and melodramatic".
Writing for the Guardian, Mark Lawson said: "The film is also manipulative, scored with a gloomy flute constantly telling the audience how moved to be. The editing is slick, but also often sly."
But he says that "despite its faults and opportunism", the programme has as much right to be shown as Diana's BBC interview with Martin Bashir or her sons' recently aired ITV documentary.
Andrew Billen gave the programme two stars out of five in The Times, and wrote in his review: "Diana: In Her Own Words was pretentious and trashy.
"But within it wronged Diana, in her sweetness and confusion, lived again.
"If you could forgive the attendant ickiness, that apparition was worth gazing upon."
Ian Hyland of the Daily Mirror was not a fan of the programme, writing: "I don't mind telling you I was livid after I watched it. That was two hours of my life I'll never get back."