I'm sorry to report that the special effects in Poltergeist do not hold up. As a result, the movie is just not that scary anymore. How is it that I thought these special effects were terrifying back in 1984? None of them look remotely real! You could argue that we'll feel the same way about Avatar in twenty years, but at least Avatar doesn't feature a tornado made by someone scribbling on the film stock with a pencil eraser.
I loved Poltergeist when I was an early teen; it was rated PG so we were allowed to watch it. We always wanted to watch it at sleepovers, but everyone made an excuse to talk or go to the bathroom during the scene where Marty rips his face off in the mirror. Why we were so scared I will never know, since it's basically a dummy head covered in wax and cheese whiz.
There's also the following concerns:
Skeletons that do not look like skeletons
"The Beast" number 666 who looks like an angry old goat wearing a diaper
A swirling orange CGI thunderstorm that moves a few hundred miles per hour but doesn't concern anyone
A ghostly hand that shoots out of a television set, courtesy of "Steamboat Willie"
A room full of swirling toys being flung around, courtesy of a giant green screen
I would not necessarily recommend you not watch Poltergeist, especially if you loved it as a kid. But you should be educated and aware: this movie is a relic. JoBeth Williams looks great, and there's some funny parts. But overall it's just not scary and the steak that slides down the counter and starts cooking looks super fake.