These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Complete Monster: ReverendHenry Kane was the insane leader of a utopian cult in the early 19th century who led his "flock" into an underground cavern under the premise that the world was about to end, but in actuality, his only intention was to harvest their souls for his own power. As a ghost, he absorbed the energy from his followers, which fused with the evil in his heart and turned him into a monstrous apparition a demon called "The Beast". When the Freeling family moves into the home built where the cavern once was, Kane tries to abduct the young Carol Anne and bring her to the realm of the dead, dubbed the "Other Side," where he could use her to attract more souls for his energy. In the second movie he keeps on tormenting the Freelings, possessing Steven's body in order to rape Diane while taking a proactive role in psychologically and physically tormenting the family as he seeks to take Carol Anne. At the end of the third film, Kane apparently abandons his pursuit of the Freelings and accepts the mystic Tangina's offer to show him into the light, but the film ends with a flash of lightning and Kane's demonic laughter, showing his supposed redemption as a sham.
Fetish Retardant: The last twenty minutes of the film feature Jobeth Williams being thrown around in her panties and a football jersey, which keeps getting pulled up; then running outside and getting muddy when she falls into the pool; then a bunch of coffins rise from the ground, and their corpses, actual corpses mind you, fall out turning the thing into a bowl of dead guy soup.
The scene with the football jersey becomes this when you realize that it is not just a cheap joke, but that the Poltergeist is trying to rape her.
"Funny Aneurysm" Moment: Several, involving Heather O'Rourke and Dominique Dunne, but the most wince-inducing is Carol Anne's remark from the second movie: "I hope I don't grow up... doesn't look like much fun."
The canary-burial scene's a lot grimmer when you consider that two of the three mourners will be dead in a few years.
Getting Crap Past the Radar: There are some hints during the film, stronger during the second half, that Dana goes on dates with guys and has sex with them, without her parents knowing: Just the day after they recover Carol Anne from the other side of the closet, Diane tells Dana that later, they'll go to a hotel, when she tells which one, Dana just goes like "oh, yes", and giving some fun smile, looking like she's daydreaming, letting us know that she knows it and that something special for her happened there and Diane saying "what is it?", or something like that. Then Dana changes subject and leaves and we don't know anything of her until the very end of the movie, when she gets out of the car screaming "WHAT'S GOING ON??!!". Look for her neck, to the left and to the right of it, you can see lovebites.
Harsher in Hindsight: An odd meta-example. The scene near the end where an invisible force pulls up the mother's night-shirt and exposes her panties gets laughs from kids. However when seen as an adult, you realize that the poltergeist is attempting to rape her. (In the screenplay it actually does).
Narm: Steve's angry outburst towards his boss at the end when the corpses of the cemetery their house was built in start bursting from the ground during the final meltdown, revealing that he'd only moved the headstones and left the bodies exactly where they were is rendered unintentionally funny by Craig T. Nelson's hysterical delivery:
"You only moved the headstones! WHYYYY?!! WHYYYYY ?!!"
The constant screaming at the end can veer off into this for some viewers.
Narm Charm: Tangina's voice is funny at first, but then you get used to it.