These days it can be hard for a good children's fantasy film or story to succeed because inevitably they are compared to Harry Potter, The Lord of the Rings or The Chronicles of Narnia. I believe that the more original, imaginative stories the better as it enables children's imaginations to grow and it keeps magic in the world.
Spiderwick Chronicles is both inventive and fantastical and the visual effects were very good. I thought Freddie Highmore did a great job of acting the parts of both Jared and Simon Grace and I believe he is an actor to watch in the future. (You may remember he played Peter in Finding Neverland and Charlie in Charlie and the Chocolate Factory).
All in all, I really enjoyed this film and even jumped out of my skin once or twice and squealed. I'd recommend this film to all lovers of children's fantasy and adventure stories.