I think there are a lot of novels that you could see as having enough Christian elements in them, woven into their tapestry, so to speak, that they might at least people thinking about Christianity in some way. Les Miserables and Count of Monte Cristo both feature men who are excessively punished for minor crimes (stealing bread), or none at all. So, both novels get the reader thinking about how just the Justice system is, and what makes a good person.
Both men are punished by the law (whether being falsely imprisoned, or not being able to live a free life in peace), and yet each man is portrayed as a good decent person.
Other books such as The Lord of the Rings have no overt Christian elements in them, but are successful because of the conflict of good and evil. To me, it’s stark how different the Lord of the Rings is from the much acclaimed new series: Game of Thrones. One is clearly the work of a devout Christian, the other the work of an atheist.
My main beef is that the characters in the Game of Thrones are all morally impaired people (they engage in any number of sins, and their goals are solely self-preservation, or otherwise selfish goals like attaining power). Not a one of them fits the classic role of a hero.
So, it does depend on the book. The newer a book is, the more likely that societies mores (or lack thereof) creep into the book, so that there is no objective morality. However, I think many of the Classics have many Christian elements in them, and perhaps that has given them staying power.