This is one of my seven favorite books. I can't pick just one of The Chronicles of Narnia.
I love the world of Narnia and its magical characters, and experiencing that land through the eyes of the Pevensie children, arriving from a war-torn home.
I love that one can read this book for an enjoyable story or one can choose to look deeper into it to do some thinking and soul-searching. Even though I've read this book 9 times (and listened to it once), I can still learn new things about it.
I love the retelling of the Biblical crucifixion story (or the "supposal", as Lewis called it). It's a way that children can be introduced to Jesus' sacrifice and a way that it can be made personal for them, as Aslan only dies directly for Edmund. It's also a way that adults can look at His sacrifice from a different angle and maybe notice some things they've never noticed before (helpful if you grew up in church and have heard the story a million times).
Someday, I'll write a review that comes closer to doing my favorite book series justice. But this is it for today. ;)