The Dark Tower is based on a series of novels by Stephen King. While I am not a fan of the series, and don't know much about how the story is told over eight novels, I was satisfied with the mashed up script that delivers the books in movie form on the big screen. The movie is a simple tale of good vs evil.
Idris Elba is Roland aka "Gunslinger" who's defended the Dark Tower for hundreds of years against the evil "Man in Black, played by Matthew McConaughy. Both characters live in an alternate universe and toppling the tower would purge all worlds, including present day earth, into darkness. The movie also stars a young boy, actor Tom Chambers, named Jake. Everyone thinks he's crazy when he starts having visions of the alternate universe and tries to warn people of the pending doom that will be caused if the Dark Towers fall.
When his parents finally decide to sent him to a mental hospital the doctor and orderly who come to pick him up are really The Man in Black's followers. He escapes from the bad guys and find a way to cross a portal into an alternate universe where he meets Roland aka "The Gunslinger."
Up until the point where Gunslinger enters the picture the movie is a bit slow and clunky, but once the battle begins to save the tower things really get moving as the clash between the two old enemies is on and popping. The two lead characters also produce some laughs. For example, when "The Man in Black" is told to "go to hell" his response is "I've already been there." Or when Roland gets a buzz from his first taste of Coca Cola in the present day world.
There's a lot to like about this movie. It's rated PG-13 for some sci-fi violence and has a run time of 1 hour and 35 minutes. On my "Hollywood Popcorn Scale" I rate The Dark Tower a LARGE.