I love An American Werewolf In London. I think it strikes the right balance between horror and humor. The scene of the initial werewolf attack on the moors is particularly intense, mainly because we the audience and the two guys know there's something out there in the dark but you can't really see it. Also, the scene on the subway is another intense one. Just getting a glimpse of the werewolf padding toward the escalator adds to the intensity. These scenes work because the werewolf is mostly unseen. What's unseen or merely suggested is often more scary than what is fully revealed. The mind's eye tends to fill in the blanks so to speak. In these scenes we feel the werewolf's presence via the characters. The scenes where the werewolf is finally fully revealed just aren't as scary or intense.

And Jenny Agutter was hooooooooot in this movie.