I watched the movie. I wanted to like it, I really did, but they left out the best ♥♥♥♥♥♥♥ part of the book. There was no fight scene in Las Vegas, and in return, no chair puns. The first half of the movie was almost the same as the book, but they cut too much out. Amy had no arc, you never even met her brother, she was just a chick with no hand that popped up on screen one time to introduce her then 45 minutes later so she could open the ghost door. It was basically like, the first hour kept on track with the book, and then they were just kinda in the other dimension. Also, didnt go into the whole body replication thing. /rant/
TL;DR: John movie was OK, left out the best part of the book, John and Dave were pretty perfect but they were the only characters that were represented fairly.