Frost/Nixon, Gala opening, London Film Festival

A rumble in the studio as Frost takes aim at Nixon

Ron Howard's Frost/Nixon is a perverse endeavour – a big Hollywood film based on a chamber play that was in its turn inspired by a 1977 TV interview by chatshow host David Frost of disgraced former US president Richard Nixon. In one way, film is the perfect medium for a drama that ultimately hinges on a single close-up when, after all his evasions and self-deceptions, Nixon finally accepts guilt for his role in the Watergate scandal. Nixon, played with real gravitas and pathos by Frank Langella, is suddenly seen at his most vulnerable. His face is a map of conflicting emotions. Seen on a big screen, this moment has a power that would be hard to match either on stage or TV. However, the rest of the film rarely matches this sequence in either its intensity or its simplicity.

For all the archive footage, flash backs and flash forwards and attempts to give Frost (Michael Sheen) and Nixon the weight of characters in a Greek tragedy, the material remains stubbornly uncinematic. The problem the filmmakers face is that this is a talking heads drama.

We may admire the performances and Peter Morgan's writing, but the nagging suspicion remains that we are caught in some no man's land between drama and documentary. The language that Frost's team and Nixon's team use is of sporting combat. Their metaphors are frequently drawn from boxing. "I shall be your fiercest adversary. I shall come at you with everything I got," Nixon tells his interviewer. At times, you could be forgiven for thinking you were watching a follow-up to Leon Gast's When We Were Kings, with Frost as the Muhammad Ali-like underdog trying to topple George Foreman. As in the so-called "Rumble in the Jungle" in Zaire, Frost takes a pummelling for many rounds while he practises his own version of rope-a-dope tactics – namely failing to ask any provocative questions. Then, as the bout draws toward a close, he suddenly unleashes all his zingers about Watergate and the champ is left reeling and exposed.

At least Howard and his team recreate the late Seventies in inventive style. Their eye for detail even extends to the mushy peas that Frost and his producer John Birt (Matthew Macfadyen) eat in the LWT canteen. "I spent yesterday evening watching you interview the Bee Gees," a startled Birt replies when he discovers that Frost wants to tackle Nixon. As he showed playing Tony Blair in The Deal and The Queen, Sheen is an extraordinarily skilful actor. Here, his characterisation initially verges on Steve Coogan-like parody as he uses Frost's catchphrases, grins toothsomely and copies that unctuous voice. However, as with his Blair, he gradually draws you in – you forget the mimicry and begin to feel for a character who (the screenplay suggests) has staked his entire career on an interview that could easily go wrong. Frost, it's implied, is only superficial superficially. Nixon's aides expect him to "pitch puffballs" and liken his interviewing style to a "big wet kiss," but the British chatshow host turns out to be the fallen politician's equal when it comes to manipulation and ruthlessness.

There is a surprisingly Gothic feel to the filmmaking. Hans Zimmer's music is brooding and solemn. The cinematography is very dark. At one stage, we may see Hugh Hefner and some Playboy bunnies in the distance, but Hefner's brand of hedonism is little in evidence here. Earlier in his career, Frank Langella played Dracula. There is a hint of Bela Lugosi about him as he welcomes Frost and his team into his sepulchre-like office with all its old photographs of Brezhnev and other foreign leaders.

As a character study, Frost/Nixon is fascinating. The unlikely encounter between two such different protagonists is drawn in subtle and absorbing style. Where the film stutters is in its attempt to stoke up a drama that wasn't necessarily there. By the time Frost got to Nixon, it was already three years since he had stood down as president after the Watergate cover-up. Nixon's political career was over. The film publicists' claim that Frost's interview with him "changed the face of politics" seems a little over-egged.

Ron Howard excels in making big, intelligent Hollywood movies such as Apollo 13 and A Beautiful Mind. Here, he arguably brings too much artillery for what is essentially a two-hander. He has an excellent (and extensive) supporting cast, including Kevin Bacon as Nixon's doggedly loyal aide Jack Brennan and Sam Rockwell as Frost's Nixon-hating research assistant, James Reston Jr. However, their parts – like that of the impressive Rebecca Hall as Frost's girlfriend – are never developed in any depth. The film is at its best when Frost and Nixon are face to face. The rest is a distraction.

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London Film Festival runs at BFI Southbank and other venues until 30 October (www.bfi.org.uk/lff, 020-7928 3232)