I have read a few books that could be classified as Christian Fiction, and I have read others that are not classified as such, but certainly have strong Christian Themes (usually written by Christian/Catholic Authors). Of the two, I vastly prefer the latter to the latter. In a Christian Culture, even one where the Christian part seems to be in decline, it is inevitable that some novels will deal with Christian ideas and themes -- you get Brideshead Revisited, the Power and the Glory, The Man who was Thursday or Death Comes for an Archibishop.
Christian fiction on the other hand really is a marketing genre like romance or science fiction but apparently with lower literary standards than either. Yes, there are occasional gems, but you have to look for them.