Oliver Stone's enthralling film about the assassination of JFK was extremely well-received for the actual filmmaking but in terms of historical accuracy, it's been widely criticised. One review called it, "one of the most appalling travesties of history you're ever likely to see."
Much of the criticism comes from the fact that, with the documentary style beginning, and use of actual footage, the movie seems to portray itself as factual, and thus misleads the viewer.
A lot of the evidence for the conspiracy was totally made up, including, somewhat problematically, the falsification of David Ferrie's confession. David, who was a real person, is played by Joe Pesci and eventually confesses to the entire conspiracy – something that the real-life David never did.
Many of the inaccuracies follow this pattern, which is why historians seem to agree that, while it's a good film, it's certainly a work of fiction.