This is one of the best movie evers, and i was really surprised when i first saw it! I never thought a movie from the 60s could be so good and realistic. Because in the movie at that time people did talk diffrent in movies, and had this fake apperance, but this is a movie that keep it to reallity great job.
The end
If you take into consideration only the kind of films made in Hollywood back then, then you are right. But in the rest of the world filmmakers like Buñuel, Fellini, Bergman, Kurosawa, De Sica, etc. were producing masterpieces in the same tone and level than Zorba the Greek for decades. Inside Hollywood studio system, perhaps only Kubrick was riding on the same wave than the aforementioned filmmakers.
That's why IMO "Zorba" is an european movie financed by Hollywood. Everything, from director, composer, story, acting, etc. are antithetical to what you could see on Hollywood's box office hits of the time such as Mary Poppins or My Fair Lady. Is not that I don't like that kind of movies. It's just that they are so different that hardly can be compared.
Zorba is a wonderful film that deserved more accolades and awards. I.e. the Academy Award to Anthony Quinn for Best Actor. Cannot understand yet how come the academy chose Rex Harrison's performance in My Fair Lady over Anthony Quinn's Zorba.