The portrait of the fiendish nun in The Conjuring 2 was scary because of its simplicity. The cold stare through blacked-out eyes is chilling; the minimalism of the two-toned demonic face matches the habit that frames it, allowing us to easily project our fears.
Now, just like the creepy doll in Annabelle, the infernal character gets its own spinoff in the expanding Conjuring cinematic universe (CCU?) in The Nun. And, just like Annabelle (but unlike Annabelle: Creation which works pretty well), The Nun has difficulty fleshing out a standalone story or generating serious shocks. The generic, longwinded backstory ascribed to the monster diminishes its power, and the imposing figure barely feels like a threat as it remains largely sidelined in its own story, only appearing for some CGI-aided face contortions and repetitive jump scares. The effective steely gaze of Bonnie Aarons, who plays the demon Valek in its nun form, gets wiped away by unnaturally large, pointed-tooth roars.