1963 was a good year for Ray Harryhausen. One of his most popular films, Jason and the Argonauts, was in general release; he married his wife Diana; and pre-production started on his next film, First Men in the Moon.
In the late 1950s and 60s, studios produced many films that we could call "Victorian science-fiction adventure" -- Journey to the Center of the Earth, The Time Machine and 20,000 Leagues under the Sea are some examples. The advance of special effects techniques and widescreen Technicolor processes allowed filmmakers to realize these fantastic worlds on the screen in a realistic way as never before.
First Men in the Moon was a departure from other science fiction films of the era. Rather than an invasion of Earth by aliens, it documents the exploration of an alien civilization by human beings. Harryhausen was a fan of H.G. Wells' book and had wanted to bring it to the screen for some time (the last film production having been made in 1919) but was unable to convince his partner, producer Charles Schneer, that it could be done in a way that modern audiences would believe.
That changed when he mentioned the idea to British screenwriter Nigel Kneale (creator of the character Professor Quatermass). Kneale proposed the idea of a wrap-around story, in which a modern UN lunar mission finds a tattered Union Jack on the surface and a note claiming the Moon for Queen Victoria. Schneer signed Kneale on to co-write the screenplay.
Unlike most Harryhausen films there are only three instances of stop-motion animation: the caterpillar-like "mooncalf", a Selenite technician and the Grand Lunar, the leader of the Selenites. The majority of visual effects are models, camera effects, forced perspective, and optical-printing layers of mattes together. The majority of the insect-like Selenites are portrayed by children in costume (the same technique used later in The Green Slime).
First Men in the Moon is a fun movie. It's very much in the vein of other family adventure films of the era like Journey to the Center of the Earth. I don't recall ever seeing First Men... on TV growing up, certainly not as often as Journey... was shown.
Trailer with John Landis commentary available at Trailers From Hell.