I saw once that the reason Kristen Stewart was so hated in the Twilight movies is because all the young women who grew up reading the books imagined themselves as Bella. They were never going to like whichever actress was cast into the role since they would no longer be able to project their own likeness onto the protagonist.

For me, it was really mostly the story changes they made so the movie could be rated PG instead of R. They also made some changes to some of the characters and the dialogue which made it come off a lot more cheesy than the book. Although, I will say, gender swapping the kids was a good move. I liked that it was the girl who was the UNIX whiz. In 1993, that felt like an especially fresh take.