One of the big differences is that in the book it tells how Ethan's father grieving about his wife's death(aka. Ethan's mom) , but in the film he seemed just fine.Also that boo radley didn't appear in the movie at all.
One of the biggest things is that Ethan and Lena didn't date in the book ,but in the movie they did. Also Marilyn's and Amas characters where merged into the same person in the movie.Ethan also played football instead of basketball.
Ethan never lost his memory in the book and the scene where Macon read Ethan's future.Also Ethan found that necklace at a different time .