Someone gave me the first book in the 'Left Behind' series to read, saying it was 'Incredible!' It was... Incredibly Awful. By far the worst written book I ever had the displeasure of barely reading. Calling it 'Fanfic' is being kind, and is insulting to Fanfic writers. Whoever the authors are, they couldn't write for a middle school newspaper, let alone a novel.
That is one of the best descriptions I ever heard of the books. I tried several times at the bookstore [when I worked there] to read some of the books, and they're just bad books. The read like an author that sat down and said "Fuck, I need to pay the bills, what's an easy sell...hey, I'll write a fanfic on the Bible and sell it as Christian fiction!".
There's nothing wrong with using the Bible or books of the Bible as plot bunnies. But at least have some fucking respect for your target audience and actually try to tell as story that's worth telling.