Originally filmed as the pilot for an aborted television series, this television movie from the creator of Star Trek stands as a strong piece of entertainment on its own. It's rarely seen today; there has never been official VHS or DVD release in America, in fact.
The movie demonstrates a lot of ingenuity (the sub-shuttle and the idea of Freud as a saint come to mind). It also captures some of the magic of the original series in its themes, but presents them with a 1970s mentality. It also has some of the camp charm of the original Trek (especially in regards to the underground cave set); the futuristic city's architectural style reminds me of a better realization of the planet Deneva from the original series episode "Operation--Annihilate!" The parade of former Trek actors -- Majel Barrett (Christine Chapel), Percy Rodgriguez (Commodore Stone), Ted Cassidy (Ruk), and of course, Mariette Hartley (whose two belly buttons here is a "gotcha" to the censors, who wouldn't permit her belly button to be shown on the original Trek) is also sure to please any original series fan.
While the film occasionally lapses into weak moments (the reactions to the nuclear shockwave at the end are among the laughable moments), it is nonetheless indicative of a series with great potential. A rare find, and well worth the watch to catch a glimpse of one of a Roddenberry series that never was. (This film was remade as Planet Earth, another failed pilot, a year later.)