Werewolf

The werewolf is the genre's most physical monster and its most technically demanding. Everything hangs on the transformation, and the transformation is the reason there are so few good ones.

The rules were invented for a film

Most of what people believe about werewolves comes from The Wolf Man (1941), not from folklore. The silver bullet, the pentagram, the rhyme about wolfbane blooming: Curt Siodmak wrote them. Lon Chaney Jr plays Larry Talbot as a large sad man who cannot stop, which is a better performance than the film usually gets credit for.

1981

Two films came out months apart and between them exhausted the form. Rick Baker's transformation in An American Werewolf in London happens in bright light, takes a full minute, and hurts. Rob Bottin's in The Howling is faster, wetter and more theatrical. Baker won the first Academy Award ever given for makeup. Nothing since has beaten either, and the arrival of CGI made the attempt pointless: a morph has no weight, and weight is the entire effect.

The metaphor is unavoidable

Werewolf films are about puberty and they know it. Ginger Snaps (2000) makes it explicit, funny and unusually well acted. Neil Jordan's The Company of Wolves (1984) runs the folklore back the other way, as a series of nested stories about what adults tell girls about men.

Why so few good ones

Because the effect is expensive, the metaphor is obvious, and once the wolf is on screen the film has nowhere left to go. The good ones are structured so the change is the climax, not the setup.