It was a mistake to . . . [spoiler]
It was a mistake to show the title creature's face, for it wasn't nearly hideous enough to justify the onscreen revulsion, screaming, and gorgonizing (petrifaction).
Obviously, nothing in real life can look horrible enough to turn an observer to stone [insert joke here].
To the contention that the audience might feel cheated if, say, only a shadow of the creature's face or the back of its head were shown, recall that effective films like The Exorcist and The Haunting (1963)--to say nothing of literary tales--showed us very little, if anything, of their central horror. To risk a commonplace, the imagination conjures worse terrors than the eye alone.