Cunningham is a talented director, but has yet to prove himself in features. Additionally, most of his credits come from documentary work, or from adaptations of true stories. Before 9/11 he directed the miniseries version of Little House on the Prairie , and his next film is a documentary about urban explorers called After ..., which is about people who sneak into "the planet's most dangerous man-made structures, just because they can." Hopefully he can make the leap into fantasy from the real world he's so used to covering.
I read The Dark is Rising when I was just starting junior high school, and it set the bar for all of the fantasy books I read afterwards. Cooper's Rising series is very dark (no pun intended), and focuses on young Will Stanton who finds out on his eleventh birthday that he must take on the Dark by himself, while looking for and gathering six different Signs of the Light. This isn't a Harry Potter book, which would be considered light and cheerful by comparison, but it is extremely rich in story and detail, especially for a book meant for young readers.
This also shows just how far the success of The Lord of the Rings has swung the gate open for the fantasy genre. Since then studios have acquired and greenlit book adaptations like Eragon, His Dark Materials, The Chronicles of Narnia (which had been in development for a long time, but the success of LOTR helped serve as a catalyst), and others are sure to follow. It's a great time to be a fantasy fan, as long as the adaptations can stand up to the rich source material.
Do yourself a favor and pick up a copy of The Dark is Rising at your local bookstore or library and read it before the movie comes out. Hopefully you'll enjoy the story in both forms.