Giant movie and book spoilers ahead. Lots of easter eggs explained here: please try to keep up
Now I'll immediately give it a sin for 30 seconds or so of logos. But I will take one off for the Tet Corporation logo.
"The Tet Corporation" is a fictional corporation that exists within The Dark Tower universe. It was founded in the 6th book of the dark tower by Roland's later Ka-Tet (Ka means destiny in Mid World. Tet is a gathering of people.) member Eddie Dean, when he buys a vacant lot from Calvin Tower, a greedy bookstore owner. Mr. Tower's best friend Aaron Deepnau Makes the corporation official With Moses Carver, and John Collum. (Who interestingly enough seem to be their own Ka-tet.) The Tet Corporation has three purposes: Protect the rose that exists in the vacant lot (The Rose is a twin representation of The Dark Tower on keystone earth), protect Stephen King so he can finish writing the dark tower books, And halt the advancement of The Sombra Corporation and North Central Positronics (Corporations run by The Crimson King's henchmen). Carver collapses Holmes Dental's assets (A Dental empire inherited by Susannah Dean from her father - who is also a member of Roland's Ka-tet. She is also married to Eddie Dean) into the Tet Corporation. Other funds came from Eddie's suggestion to Collum to invest in Microsoft in the earl 80's.
None of this is neither mentioned or even hinted within the movie. It's just an easter egg for book fans and no one else who has any idea what the hell is going on.
In the beginning we get a black screen with some white text. Unfortunately it is not "The Man in Black fled across the desert and The gunslinger followed." Which is both the beginning and end to The Dark Tower Saga. We are given instead some text describing the function of the dark tower - that the mind of a child can bring it down. Umm okay, that wasn't said in the books either
It opens somewhere in between Fedic and Devar Toi, at a place called Algul Siento (But of course the movie never mentions the names). In the books It is something like a concentration camp for people called breakers: Adult psychics who are lured from other worlds to End World with the promise of a lucrative "camp-job" at an undisclosed location.). Breakers are fed psychic energy which comes from Twins who are kidnapped from The Callas - a group of villages close to the border of thunderclap. The breakers use this energy harvested from the children to break the beams holding up The Dark Tower. One of the last great gun battles in book 7 took place at algul siento. 
What the movie does is kind of combine the two: Children are kept at a camp... Children who are psychic and are put in interesting chair which creates a giant energy beam that hits The Dark Tower. This causes an earthquake in New York which wakes up Jake Chambers, a preteen boy, from "keystone earth". The viewer then understands that the previous scene was only a dream. Or was it?
I will continue this review at a later time. The Dark Tower is a fascinating literary universe. I just want to share with the steem community by thoughts of the movie which came out based on the books. A movie which has forgotten the face of it's father.