Stephen King has never been much of a screenwriter. For all his successes as a novelist, and all the successes of movies based on his work, his writing directly for the screen is usually awkward and not particularly cinematic, and when it comes to King TV projects, the more closely involved he is, the worse they tend to turn out. Silver Bullet is a sort of odd film for King to have written himself, since it doesn't seem to be of particular personal importance, and the movie makes plenty of changes from the source novel. The director isn't a close King collaborator/admirer like George Romero or Mick Garris; it's Daniel Attias, who never directed another movie but went on to work on a huge number of TV shows, many of them quite decent. This is a pretty undistinguished debut for him, and it's not surprising that he retreated from features into the more predictable world of TV directing.
The problems do start with King's script, though. He sets the movie in 1976 for no apparent reason other than that he loves nostalgia, and he uses a retrospective voiceover from the older version of young Jane Coslaw (Megan Follows), but the idea of looking back on past events kind of disappears for most of the movie. Much of the action occurs without Jane present, so she couldn't really be telling the story, and the narration is absent for the middle of the movie. While the source novel (Cycle of the Werewolf) is structured like a calendar, with each chapter representing a different month's full moon when a werewolf emerges to terrorize a small town, the timeline in the movie is very confusing, and it's sometimes hard to tell whether days or months have passed. The pacing is lopsided, with a lot of seemingly extraneous build-up to a rushed climax.
The acting is an issue, too; Corey Haim plays Jane's younger brother Marty, who has to convince his sister and eccentric uncle (Gary Busey) that a werewolf is responsible for the attacks. Marty is whiny and ineffectual as a hero, and making him wheelchair-bound just seems like a lame bid for sympathy (and is problematic since Haim has a tough time keeping his legs immobile during certain scenes). Busey is his typically weird self, but the character is too bland to take advantage of his full capabilities. At least Everett McGill is genuinely creepy as the town's suspicious preacher, but he doesn't get enough moments to be full-on evil. And probably most crucially, the werewolf just looks silly, like an awkward guy in a costume, and as soon as it appears onscreen, any potential for scares disappears. I'm sure King had something particular in mind when he took on Silver Bullet as a screenwriting gig, but whatever it was has been lost in this cheesy, generic monster movie.
How far to Castle Rock: The movie takes place in the small town of Tarker's Mill, which seems fairly New England-y, but the state is never mentioned (nor is Castle Rock).