H.G. Wells' original novel is two-thirds Boys' Own Adventure and one-third interesting science fiction. That final third remains most compelling; it features one of the first serious attempts to describe an extraterrestrial society, and some still-relevant social satire. The 1964 film adaptation, written by Nigel Neale and Jan Read, and directed by Nathan Juran, largely ignores that portion of the book. It does, however, a passably entertaining job of presenting the rest.
Adapting classic SF to film presents several problems. The more cerebral aspects of any literature are usually the least-filmable, and often get cast aside. With older science fiction, updating the story renders it more commercial and plausible, but at the cost of some of the original's charm. An excellent example of an updated adaptation is the 1953 version of Wells' War of the Worlds. It's a solid film, but not terribly Wellsian. With First Men on the Moon, the filmmakers found a compromise.
The movie begins with a plausibly-portrayed 1960s expedition reaching the moon, and discovering an old Union Jack planted there. This leads reporters to Arnold Bedford (Edward Judd), who took part in the flight sixty-some years earlier, when he was a young man. He accompanied Professor Cavor (Lionel Jeffries), who, as in the novel, had discovered an impossible gravity-resistant substance dubbed "cavorite." In the fashion of pulp SF, Bedford's fiancée, Kate Callender (Martha Hyer) stows along for the ride on board the Victorian era ship.
The initial adventures on the moon get updated; the barren lunar landscape replaces Wells's shirt-sleeved romp on a plant-bearing world. Eventually, our heroes find their way beneath the lunar surface, and discover it has a breathable atmosphere. The plot then becomes the novel's, more or less. We meet selenites, the moon-cow, and the Grand Lunar.
Ray Harryhausen supervised the special effects, and where he is allowed to use model animation, they aren't bad. Only two of the selenites receive this treatment, however. Time and budget mean that the rest are children in costumes. These look like extras from an episode of Doctor Who, and clash with the model selenites.
MAJOR SPOILER ALERT
The changed ending, a nod to The War of the Worlds, treats genocide as a spot of humour. Granted, this is genocide of a fictional alien species which proves more malevolent in the film than in the original novel. That concern aside, the final line still feels like a cheat.
Columbia's First Men in the Moon is no cinematic masterpiece, but makes a decent, light romp for SF fans.