There are two major screen versions of Homer's The Odyssey:
The 1955 Italian film Ulysses with Kirk Douglas, 115 minutes;
The 1997 American TV Miniseries The Odyssey, 176 minutes.
Because the 1955 film is better known, I assume that is the one you are referring to.
Ulysses was filmed in 1955 in Italy, and almost every actor except Kirk Douglas speaks Italian; the original English dubbing is famous for being quite bad and mismatched. At the time, Ulysses was one of the most expensive movies ever made, and due to budget concerns, they had to shorten and modify the story.
Three major scenes are cut:
(1) Ulysses's 7-year stay on the island of Calypso
(2) Aeolus's bag of wind blowing Ulysses's ship away from the shores of Ithaca
(3) The attack of Scylla and Charybdis at sea.
Otherwise, the film is considered to be very faithful to the source material, if a bit dramatized and dumbed-down so as not to bore the audience. Most reviews mention the strong presence and charisma of Kirk Douglas, and the expensive and technologically superior (for the time) special effects. A great deal of the narrative and repetition is excised, as well as the three scenes mentioned above; they were likely cut for time and expense, as well as being the most superfluous to the plot.
there are many changes from the book and the movie
- the Cyclops didn't come help the brother in the book
- the witch was supposed to have blonde hair
- the crewmembers were suppose to turned into pigs not bears, apes , etc.