Before I get into my famous lists, let me start with the one thing I did like about the movie and that was the cinematography of going from grey to color and back. I think it was a nice visual indicator of Jonas' awareness. It was in fact something that happened in the book: the red apple, the slight changes at the Ceremony of the Twelve and I think the movie makers did a god job of using that aspect in the movie. Especially when he runs away with Gabe. The scenes he was in was in color and the scenes back in the community were grey.
Now for my list of major changes:
1) Jonas age. They changed him from a 12-year-old to a 16-year-old. This is common with movie adaptations. I allows for an older audience and more drama. I didn't mind this change.
2) The love interest and triangle scenario. This is what I minded the most. Did they really need to enhance Fiona's character to make her a love interest. She was a secondary character in the book. Lois did show hints of what could have been, but the movie took to another level and with that level come the hint of a triangle with Jonas, Fiona and Asher. I really didn't see the need for this.
3) The escape scene. This was drawn out for the purpose of the movie. I get it. An action scene to build suspense. It just didn't seem to work.
4) The Giver. I think Jeff Bridges could have been a good Giver if it wasn't for the character changes that were made. In the movie, the Giver seemed to be suffering from PTSD. He's isolated from the community, angry, has a seizure in which he accidentally gives Jonas a memory of war. The book is not like this. In the book, the Giver is a kind man who's just worn out and tired of all the memories he's contained. Something that lessens as he gives those memories to Jonas.
As I said, I didn't hate or like the movie. It just was.