The story of a man serving as an unwilling host for an extra-terrestrial parasite is a great premise for a sci-fi horror. Unfortunately, this book does not deliver. The characters are too dull to care about, the dialogue is textbook tell-not-show, and the plot doesn't really go anywhere. A central aspect of the book is the magical power granted to the protagonist, but it's not clear what the author wanted to do with it. It's clearly meant to be a central point of the plot, given how much time the characters talk about it and how it leads to the resolution, but it really doesn't do anything. No theme is expanded upon, no character development occurs, and nothing exciting happens. It's just magic for the sake of magic.
The book concludes with a retelling of the myth of Osiris in a sardonic tone and with a self insert. I'm not sure what the point of that is, either. I think the author was trying to be witty.