What can I add to the discussion of the Narnia books themselves? They're fantastic, and, as a long-time reader of Lewis's work, all I can say is that it's heartening to see that new generations are continuing to discover how wonderful the Chronicles of Narnia are, just as I did about 20 years ago. It's also great to see how many adults continue to treasure them, just as I do today.
The only thing I would say to first-time readers is the same thing that a lot of other reviewers are saying: DON'T READ THE BOOKS IN THE ORDER THAT U.S. PUBLISHERS ARE PUTTING THEM OUT THESE DAYS! Lewis always intended the Narnia books to be published and read in the order in which he wrote them: LWW, PC, VDT, SC, HHB, MN, and LB. It's true that, near the end of his life, Lewis pondered the notion of having the books published and read in chronological order -- but only after an extensive set of internal revisions.
As it turned out, Lewis never had the chance to complete those revisions. So, as they stand now, the books really should be read in the original sequence. For one thing, that's the only way for new readers to discover Narnia in the way that Lewis himself discovered it. Since Lewis never got around to his intended rewriting, the overall story unfolds much more meaningfully -- and much more dramatically -- when it's read OUT of order. For instance, part of the enjoyment of reading The Magician's Nephew is realizing just how a land that the reader has already fallen in love with actually came into being; there's an almost archaeological ("oh, NOW I understand") feel to it. If you read MN first, you miss completely that very important -- and very rich -- subtext.
I could go on: about why The Horse and His Boy should be Book #5, why The Lion, The Witch, and The Wardrobe is THE only real gateway into Narnia, and so forth. But the point is clear. I have a strong suspicion that publishers have changed the order of the books not to adhere to any wishes that Lewis himself may or may not have had, but because some corporate executive decided that less complexity would result in more sales. Publishers should have more faith in the ability of readers to appreciate complicated textual issues, even if (or especially if!) those readers are children. To read the Narnia Chronicles in the order they're in now is to deprive oneself of the most meaningful reading of the story as a whole. So read The Lion, the Witch, and the Wardrobe first -- and, while you're at it, maybe let the publishers know that you'd like to see future editions appear in the original order. But whatever sequence you follow, enjoy the books themselves!