Terrible... I'm used to movie makers butchering amazing books and crapping out the remains, but when it's done to your favourite author's work, it grates a little deeper.
Let's get the obvious point out of the way; this is nothing like the book, there's basically nothing in it whatsoever that actually matches up with the events of the book. It starts differently, we meet Tom differently, we meet Alice differently, the story itself is COMPLETELY missing, vital interactions that make us care about the characters are gone, pivotal characters are watered down to basically nothing, it's a jumbled mess that makes little sense to those who've read the book and will make none at all to those who haven't.
Truly a shame, I put off reading the book as the synopsis on the back always made it sound like it would be awful (phones are making people go crazy, Clay is on a race against time before his son switches on his phone...), but when I eventually did pick it up I picked up one of Kings best stories. This is not that story.
Dear god in heaven, The Dark Tower is next, and my soul weeps...