The books are written in the order of "The Lion, the Witch and the Wardrobe," "The Horse and His Boy," "Prince Caspian," "The Voyage of the Dawn Treader," "The Silver Chair," and the "Last Battle," as well as a prequel to the entire series, "The Magician's Nephew."
Wikipedia has a comprehensive article regarding the series, criticisms directed toward it, and their corresponding defenses.
I'm a little sad I hadn't read the books earlier, when I was young; I'm quite sure that with a much younger imagination, I would have enjoyed the books much more. I'm also very sure, that with a far less developed perception of Christian mythology, the heavy Christian symbolism wouldn't have ruined the experience for me.
The story revolves around a group of children who travel to a magical land via a portal, a wardrobe. They are referred to as the "sons" and "daughters of Adam" by the inhabitants of the land, and have a riveting adventure rescuing it from a permanent winter enforced by the White Witch of the West. One of the boys fall prey to the villain's wiles, but later realizes his mistake, but cannot be freed without a price. Aslan pays the price of the boy's freedom from the White Witch, and gives himself up to die, only to rise again.
The Christian themes were too much for me, and, it seems, I'm not alone. Some people are also saying that they were quite blaring:
"Is the world created by British author C.S. Lewis a rip-roaring piece of fantasy — or a fairy tale suffused with Christian imagery?
The book has long charmed children of any or no religion. The movie is, in many ways, faithful to the book — and faithful to the faithful — without sounding the horn of religious orthodoxy. Johnson says you will find Christian symbolism in the movie only if you found it in the book. That's fair enough, though you will find it if you look closely enough — or are told to."
This article on USAtoday.com is an interesting read. In any case, I hope the movie does well, so that they can make the sequel. Apparently, the sequel will go straight to "Prince Caspian," since "The Horse and His Boy" deviates from the central storyline of the children from "The Lion, the Witch, and the Wardrobe" somewhat.
For the fun of it, here is the link to the "Book-A-Minute" version of the first Chronicles installment. "Book-A-Minute," by the way, is only fun if you've read the books.