"The man in black fled across the desert and the gunslinger followed..." To some these words are the beginning and end of the greatest tale ever told. To most however, the phrase rings insignificant and unknown. This is one of the main risks of bringing The Dark Tower to the silver screen.
The tale of Roland Deschain has been a huge part of my life much like Star Wars and comic books. It is not however a story everyone will enjoy. It doesn't have the mass appeal of Harry Potter or the foaming at the mouth fanbase of Twilight. It is also worth noting that it is unrealistic to put some of the things in these books on film. For example, in part five Wolves of the Calla, children are stolen every twenty-four years by robotic horse riding wolves that look like Dr. Doom and carry lightsabres and heat seeking grenades called Harry Potter model Sneetches. There is also a vast web of characters from Stephen King's other works that play very large roles in the tale.
I believe at the very least, to properly translate to film you would need five full length films and a thirteen episode television series or a full eight films much like Harry Potter. None of that takes into account The Wind Through The Keyhole, the most recent novel.
Time, copyright concerns, money, and plain old commercialism are very like to make this hypothetical movie stray from the source material and the die hard fans such as myself expect the book to be honored. In my opinion the best way to breathe life into The Dark Tower is a series of anime movies or a well crafted video game that is part Red Dead Redemption and part Assassins Creed but I don't think live action is the best way to experience that moment when "The man in black fled across the desert and the gunslinger followed."