O Lord, was it a bad movie. Spoilers, but as usual I'm doing you a favor.
There were a handful of similarities to the original story. Okay, characters are George and Kathy Lutz. They're a family with some kids. They buy a house that's a steal, because there were murders in it. The house has a gambrel roof with two quarter-circle windows for the attic room, on either side of the chimney. It's haunted and/or possessed. George Lutz chops a lot of wood. A babysitter gets trapped in a closet.
Here's where we depart from the original narrative.
I define the "original narrative" as coming from the book, which I last read about the time the movie came out, the one with James Brolin and Margot Kidder. 1979. It terrified me. Granted, I was 12, and credulous, but it was nonetheless a scary story.
We're treated to the little girl walking on the roof of the house because of what "Jody" told her to do. When the babysitter gets trapped in the closet, the ghost of Jody takes her hand and puts the babysitter's index finger in her bullet wound. The babysitter is taken away in an ambulance.
(By the way, the babysitter dresses like a go-go girl--neither George nor Kathy bat an eye at this--and smokes pot.)
George Lutz has dreams about the wall he caught the dog digging at; in his dream, there's a big room behind it with a double row of dissection tables. Later in the movie when he breaks down the wall, there's a row of cells (with ghosts of torture victims in them) and a room at the end with some deranged priest or something, from the 17th century or so, cutting his own throat. The house was built where that person had tortured indians to death. This convinces Lutz to murder his family, so he gets a gun from somewhere. Cue the big tense scene where he's chasing his family with a shotgun.
But of course long before that happened, he axe-murders the family dog. Sometime between the dog's murder and the final confrontation he's doing something incomprehensible with his boat, having it in gear while tied up in the boathouse; his wife falls in the water, and her hair gets caught in the prop, and somehow this doesn't rip off her scalp--or kill the engine (because when he throws the thing into forward it promptly unwinds her hair). Trust me: if her hair got tangled in the prop, her scalp would have come right off her head--and at that she would have been lucky, because even a relatively small outboard motor generates enough torque to snap someone's neck, which would be what would happen to someone whose scalp didn't detach under those circumstances.
Mrs. Fungus was denouncing the movie as "really bad" even before we got to the scene with the haunted cells and the ghost of the suicidal priest. We gamely watched the whole thing, but the only thing keeping us entertained in that time was our own wisecracks, because that movie was absolutely terrible.
The movie could have been set anywhere, using any other characters, and been "generic Hollywood scary movie". Of course, lacking the "Amityville" name, that's all it would be, anyway.
It's a total waste of time.