My 2 older children and I are big fans of the Narnia books and have been interested in the 2 prior movies on DVD. This is the first one they have been ready to see on the big screen. They are age 7 and 9, and though that's younger than I would recommend we saw it opening weekend anyway.
We thought it was a terrific movie. We had read the book aloud over the last month to have the ideas and characters fresh in mind, and also to enjoy our own imagination's view of the story before it's forever replaced by movie imagery. We had interesting discussion afterward about how the filmmakers adapted the story. My own opinion is that new plot elements (such as the Mist, the 7 swords, temptation of the characters) offered new and appropriate depth to the story while holding the narrative tightly together as a film requires. We are interested in the religious allegories inherent in the Narnia stories, and I found them well-preserved in this film adaptation. After being somewhat disappointed by film #2 Prince Caspian for its watering down of the novel, I felt that Dawn Treader returned to the clearer focus we observed the first Narnia movie.
Yes, the movie is pretty scary and loud. The dramatic battle with the sea serpent got very intense (maybe pushing PG-13). My kids and I had agreed together to see it in 2D, rather than 3D, to take the edge off, and were glad we did. (I'm tempted to sneak back out for the 3D version...)
It's worth mentioning how beautifully imagined this movie is. The Dawn Treader vessel itself is brilliantly conceived, and the sweeping seascapes and fantastic settings make this a wonderful escape.
Thematically, I thought the issues of self-worth and temptation that the main characters contend with were believable and edifying. And the cold realization that this is Edmund and Lucy's final visit to Narnia was nicely handled (a bit of a tear-jerker for dad).