Cheap narrative tricks e.g. ordering of flashbacks and delaying multiple hinted-at scenes for artificial reader investment instead of for in-story logic. (Could have largely been avoided if narrator was a different character) 

Repetitive and unnecessary reflective sequences where the reactions and motivations are spelled out again after each scene.

Shallow and inaccurate portrayal of PTSD and cult psychology. Ex-fundie accounts give more insight.

Fair enough message about anyone being susceptible