The film doesn't measure up to the book, but that’s mainly because adapting it from page to screen proved difficult. If considered purely as a movie, it isn’t terrible; however, once the influence of the novel is set aside, what remains is an older style horror film attempting to market itself in a time when those kinds of movies require the visual spectacle of modern superhero films and a plot as simple as a children's story. It also feels overproduced for what it is. It has the feel of a traditional Drive-In horror movie but with a blockbuster aesthetic. Reducing the budget by a few million dollars and releasing it directly to video would have secured its status as a cult classic, regardless of how those who read the book might feel. The performances are solid, the special effects are impressive, and the setting is interesting, but the plot falters somewhat, and Duddits’s portrayal of an intellectually disabled character will likely be off-putting to many viewers. Ultimately, it's enjoyable B movie material that unexpectedly received a substantial budget. There are far worse options available in this era following the New Hollywood movement.

Source on TMDB