I thought about posing this same question to the board myself. Especially with all the hubbub about Dan Brown's new book. I think people are getting sick of all the Dan Brown hating, though. (To be fair, though, I'm sick of all the Dan Brown praising.
I think fiction should challenge a reader at least a little. There should be something artful about the writing and the language itself. There's more to writing than just telling the reader a simple story. Writers who do that have done little to differentiate themselves from the oral tradition of storytelling. And today we have so many mediums for simpler storytelling (comic books, radio, movies, TV). How many people here without kids still regularly read Dr. Seuss? While amusing, they were written for kids because it actually challenges (an entertains) kids who are learning to read. I get nothing more out of reading someone like Dan Brown or Stephanie Meyer than I do reading Dr. Seuss (I might actually enjoy Dr. Seuss a little more because of all his zany words and rhymes and the reader may actually learn something about poetic meter). If there's virtually nothing different between the Twilight movie and the book (and I don't recall there being any real difference), why have the book at all?