It looks like they attempted to make an inoffensive horror movie...not really in the PC sense of the word, but in the "we are going to do just enough to get an 'R' rating in an otherwise PG movie" sense of the word.
It's not really frightening. It's not really scary, it's not really gory, and the nun herself is not really ominous.
It just sort of is.
And, really, it could be a lot better.