These are short, easily read books. I have read through the Harry Potter series and the Lord of the Rings series within the last couple of years, and the Chronicles of Narnia are on an easier reading level than either of these. However, there is also a layered quality to the stories that make them enjoyable for all ages. Great books that will appeal to any age, intellect, or even religion . . . a very rare feat.
Overarching narrative, short metaphors. The ties to Christianity in Narnia are a little different than I thought they would be. Not only does Christianity provide the backbone for the fairy tale, but their are shorter metaphors interjected throughout the text. Lewis is a master at this . . . I'm already convinced that one can learn more about who God is and how He operates by reading the Chronicles of Narnia than by diving into thick theological tomes.
Seven short books . . . but I don't believe that I finished the series when I read them last time. The climax of the first book will be hard to beat . . . after all, the entire history of our world hinges on the events that lie under the surface of The Lion, The Witch, & The Wardrobe. Very interested to see how the rest of series plays out and if the suspense and narrative improves with each book, as it does in almost every other popular fantasy series.
Pick them up, and read them. Lewis is one of my favorite authors of non-fiction, and though I have read only one of his fictional works thus far I have no doubt that he will be one of my favorite fiction writers as well.
Also: attended a lecture by Alistair McGrath last December. He is currently researching and writing the definitive biography on Lewis and his works. Very excited to see this in print in the next couple of years.