First off, Tom Stechschulte's reading performance is superb, as always! As a matter of fact, his name was the reason why I picked The Oath in the first place - despite mixed reader reviews on audible.com. So performance gets a definite 5 stars!
Yet even read as well as it is, I cannot bring myself to care enough to finish The Oath. The story is fairly conventional, and I suppose the scientist thrown inmidst of the action is supposed to be the crossover element between the secular and the supernatural. It almost works, at times. Yet then there is also a prominent spiritual side to the plotline, i.e. accept Jesus and the evil won't get you.
The protagonist's brother gets killed by something mysterious at the beginning of the story because he is, as it turns out, a sinful adulterer. (He is also not very smart to take his wife on a camping trip to the very town where he has his extramarital dalliance.) Anyway, the wife is a good christian, and can fight the whatever off (she later remembers it's a dragon), calls in the scientist-brother-in-law protaogonist to investigate, and he ends up an adulterer as well, though thankfully with a different woman. In the course of the story he is saved by the town's model christian and gets a second chance - to fight the dragon who is the embodiment of the town's sinfulness.
That is how far I have made it, and it's plenty far. Any Goosebumps novel has more horror, and for evil townspeople, one can read Arthur Miller. I am not even mentioning Stephen King here because that's a no-brainer. The problem with The Oath is that its central thesis is "sinning is bad", and it's not even woven into the story covertly enough for readers to arrive at that conclusion in their own time (epitome that it would surely be).