I read the first book of the space trilogy, and I liked it. I think I got bored a few chapters into the second one though
Here's a description of the space triology, although its a bit of a spoiler:
[spoiler=CS Lewis Space Trilogy]
For all those wondering what it's about, the first book is about about a guy named Ransom who gets kidnapped by a scientist and dragged off to Mars to become a sacrifice for a monster called a 'sorn'. However, as the story progresses it becomes apparent that humans are the real monsters; in actuality, the creatures of this new world are much friendlier and better suited to a peacful life than any of us here on earth! The book includes some interesting ideas about morals and being content with what you have (not taking things that don't belong to you -- other people's planets for example
)
[/spoiler]
I also read the screwtape letters, which I found quite amusing. Parts of it can be interpreted as almost a self-help book, only you get to have fun thinking of your self-improvments as "foiling the demon's plans"