The Dark Tower by Stephen King is an epic story, spanning 7 books, telling Roland the Gunslinger's journey to the Tower; involving different genres, many characters, many worlds - a big lore. At a certain point whether you have read the series or not is probably irrelevant. If you haven't read the books, I would imagine the movie just will feel flat and lifeless, with only a few scenes from McConaughey standing out. There's very little plot and character development, which comes across as a lump of cliches. If you have read the books, you'll likely find the movie a spectacular failure, wondering how the writers managed to dumb down such promising material to a 95 minute generic action movie, and making an actor like Idris Elba overact in a character that should have endless potential. The final result is so hollow and narrow, if you have watched the trailer, you may just count yourself as having seen the whole thing. If you are intrigued by the story, skip this movie, and give the first book of the series a go.
The Dark Tower
The last Gunslinger, Roland Deschain, has been locked in an eternal battle with Walter O’Dim, also known as the Man in Black, determined to prevent him from toppling the Dark Tower, which holds the universe together. With the fate of the worlds at stake, good and evil will collide in the ultimate battle as only Roland can defend the Tower from the Man in Black.