I was pleasantly surprised.
First, I must admit that of the seven Narnia novels, I found The Voyage of the Dawn Treader to be the most boring. (Keep in mind that I was a teenager at the time.) So boring, it would take me several years before I got enough interest to finish the book and continue with the rest of the series. In the novel, the protagonists go around in this boat looking for seven lords and ... <snore>. About the only thing I enjoyed from the book at the time was the island of dreams, and they didn't actually go there!
Thus, I dreaded to watch the movie version, but was pleased to find it was not boring. Plus, they expounded on the elements I actually enjoyed from the novel. The result: a worthy sequel in an already great series.
To help the story move along, the writers introduced the idea of a green mist. It wants to devour the world, and it emanates from an island much like the island of dreams. I usually don't enjoy it when movie writers add to the novel (such as the White Witch's appearance in Prince Caspian), but in this case the green mist made a big difference.
The biggest surprise of the movie was one of the most successful character transformations that I've seen in a long time. I'm talking about the new character, Eustace Scrubb, played by Will Poulter. He starts out as a very annoying brat, which Poulter pulls off very convincingly. By the end of the movie, he turns into a heroic figure, who you can't help but to like. The transformation was fun to watch. It was natural, believable, and effective - much like Al Pacino's performance as Michael Corleone in The Godfather.
Religious Themes: Keep in mind that Lewis swore up and down that the Narnia series was not meant to be Christian literature. He was writing something that he hoped all children could enjoy. He modeled Aslan after Jesus Christ, but beyond that, no specific religion is mentioned.
Yet, you'll find plenty of religious overtones in this movie. The green mist tempts all who are weak. Aslan urges them to be strong. If you believe (here - it's the generic "believe" like in The Polar Express), then you can overcome.
Though, I must point out: if this is meant to be religion-neutral, then C. S. Lewis slipped a little when he had Aslan say, "[In your world], I have another name. You must learn to know me by that name." I'm not sure what a non-Christian is supposed to think of this line. (Unless, of course one might think that Aslan is their own father - one possible interpretation, but a stretch.)
Still, I think that anyone would enjoy this film regardless of their religious affiliation. None of the religious themes are in your face, and any moralist would agree with the concepts presented (mainly to overcome vanity, greed, pride, etc.).
3-D Effects: We chose to watch this movie in 2-D, which was hard to find. (Stay tuned to my 3-D rant in an upcoming blog post.) I did not miss the 3-D effects at all, and I still feel like I got a full enjoyment from the movie. However, there was the one long scene toward the end that I think would have been fun to watch in 3-D.
I would recommend this movie to anyone over 8 years old (there are a few scary scenes for younger children).