I recently finished "Orthodoxy" by G.K. Chesterton, and part of me really wants to read it again. If you haven't read it, I would highly suggest it, even if you're not Catholic or Christian.
The reason is simply because the brilliance of Chesterton's prose is not often equaled in literature. His mastery of the English language is something the rest of us mere mortals only dream of. Line after line I was taken aback by the constant stream of uninterrupted thought, which seems to be have been written barely as quickly as Chesterton could think it. It gives the reader the feeling of being perpetually doused with an onrush of brilliance by a narrator of unparalleled imagination and intellect, just as one would be nearly overwhelmed by the beauty in a beautiful piece of art.
In the midst of this cascading rhetorical waterfall, Chesterton presents his views on various abstract concepts which often plague modern thinkers. He doesn't get into the "nitty gritty" of the subjects themselves; instead he explains enough of the issues to make his arguments make sense. He treats each subject delicately and forcefully; he does not mince words. What struck me is the way Chesterton writes so that one begins to wonder how anyone could think anything different.
The book itself is not a treatise in support of the specific doctrines of Catholicism/Christianity in-and-of itself. Rather, it is an explanation of how Chesterton came to believe how he believed. Thus, in some ways it is autobiographical, while it maintains some of the features of a philosophical essay.
So, don't pick this book up if you want a catechism, for it is not. However, if you want to know how one of the most brilliant and respected writers of the 20th century came to abandon his old beliefs - or absence thereof - in deference to Catholicism, then read this book. If you want to read some of the most flowery and remarkably eloquent writing of the past 100+ years, read Orthodoxy. Many times during the course of reading I had to remind myself that it is a work of non-fiction, for Chesterton writes in such a way that even making a sandwich would seem dramatic. Trust me: you won't be disappointed with this semi-autobiographical treatise.