The Sparrow tells the story of a group of people who are sent to explore a new planet and get to know the people and culture there. At the beginning you already know that something went wrong in the mission, as you introduced to the sole survivor - a priest who is beat up and broken. The chapters that unfold the wonder found in discovering and venturing a new planet are juxtaposed against the priest's processing and sharing (or lack of sharing) the tragedy that occurred on the planet. And yet even as it is tragic, it is also hopeful.
Although it is a very good story, it is also a difficult story - the events that happen on the planet are disturbing. They describe a culture that uses another culture/race to meet their own desires and needs. And the book questions the assumptions we make about what is appropriate and reasonable. In their interactions with the other cultures, they naturally makes mistakes - things they did even with the best intentions - and being as careful and sensitive of the other cultures as possible.
It does a very good job of discussing how God reveals himself, how people relate to God (and spiritual) and what can happen when one's expectations of God are completely demolished. It is the story of a slow healing and a growing awareness that there is no simplistic way that one can see God's working in the lives of people.