The subway scene is a moment of horror perfection. Hiding the werewolf and showing only an absolutely terrified man charging through nightmarishly empty hallways is good...but then it becomes GREAT. A wide shot from the top of the escalator -- the sounds of breathing, growling, and the hum of machines -- the American Werewolf lumbering its thicket of mass off in the distance..but not too distant.
And the fact the movie manages to be funny without undermining itself is a minor miracle. Nazi werewolves, pop songs, and a porno theater with ghouls would collapse a lesser film, but instead we get a believably wild, macabre European trip gone terribly wrong. Of course the movie is set in Britain -- it has an old world charm where werewolves just might still exist, and it's a place where black, cynical humor can thrive. And that's what this movie has in spades -- an almost nihilistic glee at breaking poor, doggish David down.
Even when it misfires a bit (in a movie with werewolves and ghosts, what boggles me is how hospitals are just cool with nurses taking patients home), it's a movie with a drive. It sets its problems, it sets its stakes [no, don't worry, no vampires], and then sets all hell loose. An American Werewolf in London is a wonderful throwback to the childish glee of just letting monsters rip people apart, and the poor SOB who deals with the morning after.