These books completely changed how I think. Lewis took phenomenal concepts about the Fall of man, redemption, and even higher powers (we call them angels and demons, they are here known as eldila) and wove them in to a fantastic science fiction.
The writing is a bit hard to stick with, the style found in Narnia a little more grown-up and long explanations. But the story is fantastic. Traveling from Earth (Thulcandra), a linguistic's professor, Ransom, is thrust into the world of Mars (Malacandra) where frightening giant otter-beaver-creatures roam as do classic, skinny and scary aliens. He learns much about their world, civilization, and our world there.
In the second book, Ransom again finds himself in space, traveling to Perelandra (Venus), a planet new born facing sin for the first time. In the final book, Ransom bands together with other believers to attempt to save our own Earth from an institutionalized threat.
Lewis deftly weaves together Christianity, Greek mythology, and Logres (Camelot) in this series. Elements of Narnia show up and Lewis' famously well-thought out doctrine colors the tale while his vivid imagination takes it beyond anything in this world.
Life on Thulcandra will never be the same.