This is a classic movie. One thing I want to point out is that the disappearance of the little girl into another dimension was the premise of a classic Twilight Zone episode aired in 1962 entitled "Little Girl Lost". If you come across it in reruns, check it out. Many of JoBeth Williams' reactions are seemingly taken from this Twilight Zone episode about a little girl who disappears into another dimension during the night. Poltergeist has many more elements to it( the poltergeist, of course, the monster, the tree outside, and the appearance of the Indian burial ground), but the initial disappearance of the little girl is straight from this Twilight Zone episode.
Review of Poltergeist
