It's just that it could have been really good. In many places, it is that good. A film, like any work of art, conveys its meaning by structure. Its meaning is not just the things that it explicitly says. A film maker can't make things happen just by saying that they're so.
Meaning arises out of interaction.
Eve's Bayou shows several illustrations of how this principle works and also of the cost of ignoring it. For a positive example, we might look at the character of Elzora, the witch. If we were to look at her out of context, she would appear incompletely developed as a picture of a human being. A whole film full of Elzoras would be pretty shallow, like Halloween . But taken in context, she's a carefully judged part of this film's economy.