With some familiar elements of classic thrillers plus some creative turns, this is an unusual and effective thriller. Patty McCormack is memorable as young Rhoda, and the rest of the cast succeed in making their characters react believably to some nearly unbelievable situations. The story moves slowly enough to build suspense carefully, while still holding your interest the whole time.
For this kind of story to work, it has to keep the tension and uncertainty without becoming obviously implausible or annoyingly overplayed. In "The Bad Seed", we see the tension and fear that build in the characters as the story develops, but events also unfold within an atmosphere that otherwise would be peaceful and normal, making for an interesting contrast that helps to maintain a good balance.
Unlike the many banal movies made in recent years about serial killers and the like, "The Bad Seed" also contains some substance. The characters, especially the mother (played by Nancy Kelly), not only have to make difficult decisions, but also must fearfully attempt to understand the reasons for everything. It's a good example of how well a thriller can work when carefully made without a lot of extraneous elements, and it's a demonstration that a movie can have a tense, dark story without being shallow or superficial at the same time.
