The Girl who Leapt Through Time.
Not saying it was a bad-movie - it was a great movie - but I think it was only based very loosely on the book. I can't remember the book very well (years since I've read it. It was actually an internet translation) but I don't think any of the characters were called what they are in the film, and the main-characters look nothing like they do in the book-editions covers, and in the movie, the romantic relationship between the protagonist and one of the other characters was alot more playful in the movie - infact, it was hardly romantic.
I'm not sure why, but those really annoyed me.