After a honeymoon period lasting nearly 20 years Pixar Animation Studios appear to have hit a rocky patch with Cars, their latest cartoon spectacular. Tipped as one of the year's biggest hits, the film opens in the US this Friday and in the UK on July 28. But early reviews are not encouraging.

Directed by John Lasseter, Cars tells the story of a rookie sports car (voiced by Owen Wilson) who becomes stranded in the homespun township of Radiator Springs, off Route 66. Expectations for the film are high following the success of The Incredibles and Finding Nemo, but critics appear to agree that Cars is not in that class.

"With Cars, Pixar's enviable run of creative triumphs comes to a skidding stop," said Variety. The film, it added is "a dusty near-two-hour ride" and "the action keeps running out of gas." For good measure, the magazine went on to argue, "Lasseter discovers that there are only so many car puns he and five other credited writers can exhaust."

The Village Voice agreed that the film has a "turgid pace, with all the traction of a boxcar going uphill in molasses." The film was "a disappointment, following the grown-up comic-book that was The Incredibles."

Many reviewers also felt that Cars' plot was too indebted to the 1991 Michael J Fox comedy Doc Hollywood, in which a hotshot Los Angeles doctor learns a new set of values when he is stranded in an average American town. "It just rips off Doc Hollywood, almost note for note," said Christy Lemire of the San Francisco Chronicle.

The Hollywood Reporter was kinder to the film. "It might not be up there in The Incredibles/Finding Nemo/Toy Story stratosphere," it admitted. "But the charming Cars is nevertheless a thoroughly pleasing way to mark Pixar Animation Studios' 20th anniversary.