Whole plot constructed on cheap shock value and twist. One of the main characters doesn't even have a personality, and when story already close to the end he decides give us explanation and give her some 'development'. Also, Eren's character development is a joke. Isayama just skipped 3 years of the story and then filled the blanks with flashbacks, which is the most cheapest tool author can use to develop a personality.
AoT should have ended with everyone dying like Isayama originaly planned instead of dragging out