Let me start by telling you what I liked about the movie and then tell you why I would never recommend the movie without some qualifications.
First, the characters are a little predictable since the heroes are underdogs and misfits at their school and at home. But I could not help but love the characters in this story. They were genuinely likable and part of this is because of the good acting done by the actors. The smile of the actress who played Leslie is infectious and magical.
Second, the friendship forged between Jess and Leslie, our hero and heroine is powerful. Again, I work with Junior High and cannot notice how "fictional" such a friendship is. A friendship full of trust and actually the friends being friendly? How about a friend who genuinely shows selfless generosity? To be honest, all my students know is cruelty and humor and usually those are mixed. This is why they are so enamored with horror movies and laugh at each other so easily and very rarely show compassion to each other. Watching the friendship between the two main characters in the movie gave me a little hope for if it can imagined then possibly by God's grace it can accomplished.
Third, the movie is simply well-made. Thanks to Weta, the special effects guys responsible for The Lord of the Rings and The Chronicles of Narnia, we have some incredible visuals born of the imagination of our heroes.
Now for what I did not like. I have not read the book so I cannot comment on it specifically. But the movie puts a bulls eye on the back of evangelical Christianity's belief in God's judgment, takes aim and fires. And it takes a cheap shot at that. It uses the conversations of extremely cute children about whether God would damn sinners to hell. The children who believe are the ones most easy to laugh at in the scene while the child who will not believe God would be doing such a thing is the very one with the magical smile. Thankfully, my kids saw it for what it was and discounted it. They are thankfully mired enough in a biblical worldview to be happy with the God as he is presented in the Bible.