One of Lewis' fantastic pieces of fiction. This book is an allegory of human responses to God. It is set in Heaven and Hell, but is not meant to be a literal description of what Heaven and Hell are actually like; rather, Lewis uses those places as the setting because he is talking about the nature of true reality, which is beyond our current limited world.
Although the descriptions of Heaven and Hell are important, the characters are the key to this little book. Each character represents different peoples response toward God which is a result of their attitude toward life. Their is the self indulgent, the lazy and those who somehow got it. What Lewis does so well in all his books, and especially in this one, is to make the reader identify with each character. As he describes them you immediately start to think of people you know, but even more skillful than that, his best and most subtle character is you. The book is set from what appears to be his perspective, but you automatically identify with the character so that you don't even realize it, but in your imagination you are seeing what it would be like if you had gone from Hell to Heaven and were meeting all these people.
The book does give a hint of universalism (the idea that all people will one day be saved), but I wouldn't let that get in the way of enjoying the wisdom that will be gained from reading this book.