Game of Thrones was nearly "destroyed" by pirates illegally streaming HBO content
(www.forevergeek.com)
A surprising amount went wrong.
While there are a sea of complaints, the biggest for me was that all of the characters stopped having internal logic. Take Jamie, he had a character arc moving from a vain knight avoiding responsibility and having an incestuous relationship with his sister, to having depth, showing that he was wracked with guilt for breaking his oath to help people. Falling in love with a woman for her character and who she was. Being responsible and honorable again. Then the last season came around and he dropped all of his growth to be with his sister.
It's like D&D decided that there would be a cool scene of him dieing with Cersi and didn't care how he got there.