They didn't change too much and they stayed pretty true to the book.
The same thing goes with the characters. I'd like to talk a bit more about Theo James who played Four.
Four is a pretty complex character to play. He have this harsh personality that you don't wan't nothing to do with. He have these high walls around him, and I think those who have read the book knows why.
But Four is more than that. He does have feelings (surprisingly enough).
He just doesn't show them in a obvious way.
I'll give the movie 4 out of 5 Dauntless cakes.