As the title indicates, this books plays off of Christian themes heavily. The very idea of "the fall" is a fundamentally Christian notion of lost innocence (which is very much at the heart of this work); "Jean-Baptiste" - "John [the] Baptist" in English - describes himself as a type of prophet crying in the wilderness but refusing to come forth; the bar he frequents is described as a church (and one could argue that, by extension, his life in the bar is something of a participation in an inverted communion); entire discussions about redemption, forgiveness, and repentance fill the pages of this work.
Despite all of its religious imagery and imagination, however, it is a work that is completely devoid of any notions of real redemption, forgiveness or love. Clamence's/Camus' view is basically that this world is, indeed, fallen but that there is nothing else.
It is interesting that an entire discussion about the death of God takes place within this book. As Camus - like Nietzsche before him - notes, without God all meaning and transcendence is lost. The picture Camus paints of such a world is indeed compelling if God is dead; as Clamence says - tragically - at the end of the book, he would permit himself everything all over again but without laughter the next time. A world devoid of laughter is a world devoid of love; a world devoid of love is a world devoid of transcendence; a world devoid of transcendence is a world devoid of God.
This book is a heavy work that attempts to carry the weight of the world upon its existential shoulders. It is one of the better places to start if one is interested in getting a feel for existentialist philosophy and literature, as well as a post-Nietzschean worldview.
Upon finishing this book, one should listen closely to the sounds of a haunting silence, born of a world without laughter, and ask one's self whether or not that silence is compelling. Is it what one wants to hear? Is it what one does in fact hear? Perhaps ironically, it is only in such absence that the whisper of faith, hope, and love can be heard; indeed, fallenness cannot be the totality of being.
A viewpoint that denies laughter is, in the end, a viewpoint worth looking past, over, and beyond: in short, transcending.
One of those books that you have to stop once in a while and reflect on what message has been communicated. What is the hidden message behind all this, and how would that imply to me...
Even if you are not into these kind of books, I believe you should try reading it, quick reading, easy to follow through, and more than anything else enlightening.
Some years later, when I read Dostoevsky's Brothers Karamazov, I realized that he had managed to convey what Camus does in this book in a single two page conversation between Father Zosima and Katerina Ivanovna. Though I still like this book, this is mainly for stylistic reasons now.