My go-to Carpenter movie is Ghosts Of Mars.
Well anyway, moving right along - I Kill Giants. The book presents a cute metaphor for dealing with things beyond your experience, but the film bets hard on only one interpretation of that material (that the fantasy elements are all imagined), thus changing it from a whimsical tale of a young girl learning to grieve in her own time and turning it into a story about a bullied child's struggle with dissociative paranoia that leads her into violent outbursts, self-harm, arson and life-threatening situations, and the film offers no resolution to this new interpretation of the material rather than a slightly disturbing allusion to an offscreen visit to some kind of Pray The Gay Away camp from which the protagonist has returned with a more socially-acceptable attitude and appearance. The book gets away with a trite wrap-up that the film can't replicate, so they don't try, thus lots of characters and subplots are just abandoned and never resolved, like the school bully or the bratty brothers who just disappear from the film at some point. The kid actors are good, but the adults are... uhhhhh... well, the kid actors are good.
I get the feeling they just tried to replicate other entries in this kind of slightly depressing subgenre of literary adaptation (Bridge To Teribithia, Where The Wild Things Are), but while that might work in the realm of saturday morning cartoons where screenwriter Joe Kelly (who wrote the original book!) usually plies his trade cobbling ideas, scenes and jokes from other things together and calling it a day, in practice with something that demands more focus and a tangible start and end point and a director not keen to replicate any of the book's more memorable fantasy visuals, it results in a drab, unfocused and joyless film.