The Fault in Our Stars shows why the best books should never be made into movies. There's nothing particularly wrong with the film that just opened. It's just that it's a film and not a book.
First, there's the fact that it visualizes all of the stuff your mind was responsible for visualizing when you were reading. And so you are less involved, more passive.
Then there's the fact that how they visualize it can never meet every (or any) reader's vision. I don't even know how how I visualized it, I just know the film is wrong. From the moment I saw photos of Shailene Woodley and Ansel Elgort, who play the two main characters, I reacted against their mushy, nondescript pretty faces. And would it kill Hollywood to hire actors as parents who have even a passing resemblance to their "children"? Not to mention the locations, props, cars… It's all so shiny and catalog-perfect.
Something also seems to have been lost in the wonderful exchange the teenagers have with the reclusive writer they are pursuing, hoping for answers to their questions about his ambiguous novel. Willem Dafoe as the author is probably the best thing in the film, and yet I found the outcome of his interaction with the main characters unsatisfying, while in the book I thought it was brilliant. Maybe, once again, I, as a reader, was filling in the unsaid and unwritten, while the film puts it all out on the screen, revealing that it's not as revelatory as I thought.
Finally, the film makes it clear the male ingenue Gus is a Mary Sue, which I somehow missed in the book. Maybe it's a loss of complexity from the translation to image, or maybe he was always like that and I just missed it, caught up in the emotional involvement of the novel.
Or possibly I would have thought less of the book on a second read. But now the movie interferes with my ability to do that assessment without hearing Shailene Woodley's voice in my head. Darn.