American Werewolf has a great sense of humor to compensate the often bleak story line (it never ends well for the werewolf). The movie opens with two American students David (David Naughton) and Jack (Griffin Dunne) hiking through the English countryside and are attacked by a werewolf. Wiseguy Jack perishes, but David survives.
While recuperating in the hospital David experiences terrifying nightmares and receives visits from an "undead" Jack. Dunne often gets the best laughs and is quite menacing as a ghoul. David begins a romance with a sympathetic nurse wonderfully played by Jenny Agutter. So all seems well until the next full moon.
American Werewolf works for me, because like The Exorcist and Rosemary's Baby, there's a strong sense of reality thanks to the on location shoot. When watching those films it's hard to believe something supernatural will happen, making it all the more terrifying when the scares hit. The unforgettable transformation sequence, which took weeks to film, stands alongside John Carpenter's The Thing for most intense pre-CGI effects.
Landis wrote a great homage to monster movies of the past. The film rightfully earned its "R" rating with the gory effects and raunchy humor.
An American in Werewolf in London remains the best of its kind for the jarring shifts in tone - a first rate entertainment for the Halloween season.
Notice how the trailer plays up the horror elements.