A large percentage of the modern horrorscape is devoted to possessions, hauntings, and the intersection between the two. So it makes perfect sense that people would comb through the documented cases of such things and put together a movie around that. After all, nothing adds verisimilitude to a project like slapping “based on a true story” to the tagline.
Thusly, The Conjuring, in which actual people named Lorraine and Ed Warren set out to assist an actual Rhode Island family which consists of two adult Perrons and their five daughters, who mostly like to play Hide&Clap and get haunted by restless demons who are hidden implausibly poorly in a boarded up basement. Which doesn’t sound so implausible, I know, except that the house’s furnace is in the basement, and the first time it got cold (demonic or regular), someone was going to go looking for that, you know?
The thing about a true story is, you’re constrained by it. If you’re trying to be anything like faithful to the narrative at all, you will have sudden stops and starts that don’t really fit the expectations of story progression, and no particular themes, just a series of disconnected events and an unreasonably creepy doll. The upshot of which is, this is a perfectly serviceable scary story about which I have basically nothing relevant to say.