I haven't read the book, so i came in the cinema having no clue at the plot. Story wise it was ok, it kept me interested throughout the movie. The only thing I didn't like was the acting of the protagonist, I don't if it was intentional to make him awkward or he is really that bad at acting. Regardless, it is a feel good movie, and a unique fantasy movie too!
I know it was done to promote the movie, but I think it's just too bad that they switched Emma and Olive's peculiarity and made Olive older. They stopped following the book's plot after Dr. Golan (Mr. Barron) followed him inside the loop.