An American Werewolf in London is part of a very honourable cult genre: the werewolf / vampire film. The rules of these films are standardised. Vampires are blood-drinking living corpses whose mrer bite can make you one of their number. Werewolves are people who turn into wolves, or wolf-like humanoids, at every full moon, and their bite turns other humans into werewolves. Vampires can only be killed by fire, removal of the head or a stake through the heart. Werewolves can only be killed by a silver bullet or the SAS.
An American Werewolf in London was directed by John Landis, an American whose most notable cult feature is The Blues Brothers. American Werewolf was influenced by Dead of Night, the classic British horror film, and it contains every conceivable song in which the word 'moon'appears. It features a nice cameo by Mr Frank Oz - Muppets genius and director of the very funny Dirty Rotten Scoundrels - as Mr Collins, the man from the US Embassy. You can also spot Rik Mayall playing chess in a pub called The Slaughtered Lamb, and Brian Glover who is a very good actor.
It's a weird mixture of naieve comedy and apocalyptic violence with an abrupt ending. If you sit through all the credits, you will see that the film is dedicated to 'Their Highnesses the Prince and Princess of Wales on the occasion of their marriage'. Only an American could be that patriotic.