It is billed as a "science fantasy western" that continues the themes of the Dark Tower novels. Part of the problem may be trying to capture the essence of a series of novels that spans King's writing life. Critics have denounced the plot as incomprehensible and unfaithful to King's novels.
The film features Idris Elba (fans of The Wire will recognize him as the actor who plays Stringer Bell) as Roland, the last of the lone Gunslingers. Matthew McConaughey stars as Walter o'Dim, the Man in Black, an ageless deceiver and sorcerer.
The Dark Tower film has an interesting history. It started production in 2007 and has had three successive directors: J.J. Abrams; Ron Howard; and finally Nikolaj Arcel (with Howard in a production role). A follow-up television series is planned for 2018. (Sources: Wikipedia and Rotten Tomatoes)