This is not a review, because I literally just got home from the TFiOS movie and I haven't articulated very clear feelings about it in my head yet. But. (Spoilers, obviously.)
One of the things I think about whenever I see a movie adapted from a book is the pacing. I call it the Harry Potter test.[1. I have literally never called anything that in my life before now, but this feels like it should have a 'test' name.] From film 1, the Harry Potter movies have an incredibly jumpy, disjointed feeling to them, like huge chunks of time are just plain missing. I think it's because (a.) the books are huge, and (b.) they take place over a very large span of time. I don't know whether failing the Harry Potter test indicates a poor adaptation or a story that isn't well suited to be a feature film, but it's a symptom I've only ever noticed in book adaptations.
The TFiOS movie did pretty well, but it still had a little bit of that going on. It may not have even had anything disjointed going on that I would have noticed if I had never read the book, but, having read the book, there was stuff I noticed missing -- like Hazel talking about how she envied Gus's nickname-able name, leading Gus to call her Hazel Grace the whole movie.
To completely change the subject, Van Hauten's scene, when he played that Swedish hip hop song -- Bomfalleralla -- made a lot more sense to me than it did in the book. Maybe that's not good, because it's clearly not supposed to make sense, at least to Hazel and Augustus, but actually hearing the song while Van Hauten was talking about it made it pretty clear to me what I think he was talking about. He said the meanings of the words didn't matter, that it was nonsense. Obviously that's really dismissive of Swedish speaking people, but incomprehensible anger is pretty much what I figure Van Hauten meant for the characters -- all the characters -- to have felt.
Willem Dafoe was an awesome Van Hauten, by the way.
I have more thoughts but it's late and I can't string them together. More to come later probably eventually.