Gary Raymond as Acastus and Todd Armstrong as Jason
The film is well-designed both in screenplay and in art direction. The crew got permission to film in ancient ruins. In fact, they got permission to climb around on them; something that would never happen today! The Argo has a classic look that would be copied again and again after this film.
In fact, this film establishes many fantastic archetypes of design and story that would be copied in mythological films and television series for decades to come. Though I think the casting of the Olympian gods was a bit off (they seem too young to me), the manner in which they're presented is very effective. They watch events from Mt. Olympus in a pool of water and move mortals about on a game board as if they were chess pawns. These are ideas that would be used ever after in portrayals of the gods on film, including in another Harryhausen film, The Clash of the Titans.
Niall MacGinnis as Zeus and Honor Blackman as Hera
Though there are many departures in story from Apollonius' Agonautica, this is a strong adaptation for film. Many of the darker aspects of the story dealing with Jason and Medea's relationship were not dealt with at all. They would bogged down the adventure of the story and probably not been popular with audiences of the day.
Of course the real reason for the success of this film is Ray Harryhausen's fabulous special effects work. People never remember the directors or writers of Harryhausen's films, they remember his name, and for good reason. Harryhausen's work in this film is nothing less than stellar. Characters like Talos, the Harpies, Triton, the Hydra and the Skeleton Warriors have inspired generations of filmmakers.
This is a fantastically entertaining film that holds up well all these years later. Bernard Herrmann's score is stirring, Chaffey's direction is engaging and Harryhausen's creatures are amazing!
The film has been very well-preserved. I have it on DVD as part of the Ray Harryhausen Signature Collection. This is a terrific boxset. The art is great and there are some bonus interviews with Harryhausen that are almost as fun to watch as the films themselves.
The largest public exhibition of Harryhausen's work is on display at the London Film Museum until June of 2011. More details can be found on the artist's official website.