Not Bad
There are problems. There is a monster but we don't see much of it and what we see is not good. Also, and rather oddly, we see the monster around the mid point of the film and it is virtually missing from the rather weak finale... Which seems like the wrong choice.
On the other hand most of the actors are good and that's beyond James Earl Jones and Mel Ferrer, who are great. And I appreciate most of the character writing; dialog and actions, they seem like real people. Even if James Earl Jones quotes from Othello a few times too many.
The film has a little bit of the folk horror vibe of The Wicker Man and the sunny Greek village setting is rather nice.