So I actually watched the film before I read the book. So far, I think it was pretty accurate, except with some parts like the cave scene, the after cave scene, and I think those details were ok to be deleted in the film.
But what I preferred more with the book is how I understood the protagonist's point of view more. I love how it's emphasized that having any scent, he knows nothing about his existence, and that's what made me feel so sorry for him.
So yeah, go read the book because it's awesome and amazingly disturbing and artistic in every way. :)