I haven't read Stephen King's The Dark Tower series this is based on. Apparently this is a sequel. But as far as I can tell, they've taken a massive epic and reduced it to a short and trivial fantasy movie for children. Which is doing a disservice to the children's movies that are coming out these days: most of them have more brains than this workman-like foolishness.
The three main characters are Roland Deschain (Idris Elba), Jake Chambers (Tom Taylor), and Walter aka "The Man in Black" (Matthew McConaughey). Jake is a human boy on modern-day Earth who has visions, which has led his parents to think he's insane. Roland Deschain is the last Gunslinger, the protector of the Dark Tower, who is seeking revenge on Walter (who killed his father). Walter is an evil magician who wants to open the universe up to the demons that live outside it by destroying the Dark Tower - and to do that, he's looking for a child with Shine. What "Shine" is is never really explained, but apparently you can send thoughts to people.
The problem is, it should have been a TV series - a long one. Not only have they squeezed it into 90 minutes, they've made something with the brains of a toad - and the repeated recitation of the ludicrous Gunslinger's creed. "I do not kill with my gun; he who kills with his gun has forgotten the face of his father. I kill with my heart." (It's longer than that, but that's quite enough.)
I can't recommend this one for anybody.