Even before this movie was released in 1981, critics bashed it saying "stop motion is out". Stop motion is the technique by which a small model is moved a fraction of an inch, one frame at a time, photographed, and when the frames are run together, it appears as if the object is moving. Computers were helping animators move models and "Go motion" was born (it was used in 1982's Dragonslayer- resulting in very smooth animation).
Of course, the movie going public LOVED this film, making it a big hit, leading to a 1982 rerelease. I saw this movie in a theater at a 10pm show filled with adults, and the audience cheered, laughed and applauded during the credits. To this day, this remains a popular film.
Yet it also remains one people like to poke fun at. Arnold's LAST ACTION HERO has a scene where a teacher shows her class HAMLET, sarcasticly noting that Lawrence Olivier was in this movie before his "epic" CLASH OF THE TITANS. Joke if you must, but the animation scenes in this film rival any in stop motion history. Ray Bradbury picks the Medusa scene as Harryhausen's best.
Based on Greek mythology, the script is actually a love story: a hero tries to save his true love from adversity (in this case titanic monsters). The animation is integrated well into the story, and not just a showplace for Harryhausen's talent.
The film still holds up today, even the effects. When computer animation is done on the cheap, as in many of today's lower budgeted films, it looks cartoony. Stop motion employs a solid object, and is truly amazing if done right.
Small children might find some of the monsters frightening, but all other fantasy fans will have a great time.