As mentioned before, the Dark Tower series is bigger than just the eight official novels. There are comic books and novellas, too. Even that might not be enough to daunt the serious adapter, but you know what? It's even bigger than that. The Dark Tower series is, for Stephen King, a kind of culmination of his entire oeuvre. He uses characters and events from many of his other books in connection with Roland's quest. In order to get the full experience, there would have to be spin-off movie adaptations of The Talisman, Insomnia, Rose Madder, The Eyes of the Dragon, From a Buick 8, The Regulators, and so much more Dark Tower-related material. To do so would be more than impossible, it would be downright insane. The only way the whole story can ever be absorbed is by reading more than half of King's expansive collection.