One of the biggest problems I have with this movie is the creatures. Supposedly, they were trapped in a huge cavern for eons. Then, once opened by explorers, they quickly destroy the world. Europe fell as well as Asia within a short amount of time, days maybe. So the problem is this. Where did they get food from while they still lived underground? How was there billions maybe trillions of them trapped underground, since they killed Europe and Asia so quickly? What is their food source underground. Where are those creatures at? Those creatures would have also developed skills and mutations to combat the bat-like creatures.
One other thing I would like to point out is the description for the movie is wrong. "However, they discover a cult who are eager to exploit her heightened senses." The cult didn't want her for her heightened senses. They want her because she is fertile. They write as much on the tablet. "SHE IS FERTILE". Nothing is said about her senses. In fact nothing is ever portrayed of her having heightened senses. The cult leader sees them in a store signing to each other. He then offers them a place in their group. They decline and leave. The cult follows them to the place where they are staying and tries to get them to join again but in that scene the cult leader writes down that "she is fertile". Nothing about her heightened senses.