Let me just say this right out front: I am a fan of the Susan Cooper books that this movie is based on. I haven't read all of them yet (which reminds me...), but I've definitely read The Dark is Rising, the book which the movie The Seeker: the Dark is Rising resembles.
So, when I heard that there was a movie in production, I was very excited. Yes, I realize that it's partly a scheme to capitalize on the success of many book-to-film adaptations. The booklover in me also kinda hopes to increase literacy, but meh.
I'm just hoping that I didn't actually pay to see it. Don't get me wrong, the effects were awesome, and Christopher Eccleston was wonderful. The plot, on the other hand.... was disappointing. Just... really really disappointing. With the material that's available in the book, it could've been a lot better.
Parts of it was just too rushed, information was given too fast, pacing was just not well done. In a lot of ways, it relies heavily in the special effects area, which isn't too bad. I'm pretty sure that there's movies out there that have as good as special effects and better plots though.
So, final verdict: Eh. If you have the money and are bored, sure. But I'd rather pick the book up at the library instead.