There were many things in the eighth season which went wrong and made the fandom really upset and angry.
1. Character change of Sansa.
Sansa always being an innocent, gentle,caring and reserve from season one to seven suddenly becomes responsible, fearless, rude and diplomatic. In season 8 Sansa gives more attention towards the disagreement between her and denareys instead of focusing upon the defeat of cersie and taking her family revenge.
2. Bran being not Bran
After coming back from the cave, or becoming the three eyed raven there was a sudden change in the behaviour of Bran. Tina after helping him in his journey and saving his life many times, only got a thank-you from Bran was very disheartening. And seeing his family reunite again he was expressionless being completely weird for everyone.
3.Arya not getting a chance of killing Cersie.
After getting trained from so many season, preparing to fulfil her list of people she needs to kill in order to avenge her family, she is unable to kill the last living person Cersie was unsatisfactory.
4. Jamie leaving Brienne for Cersie.
when we talk of switching the characters then Jamie lanister is also one of them. Portraying negative character from season 1 and being devoted to Cersie suddenly choose his moral ethics over her and decides to fight beside starts against the night king was a surprise for GOT fans.
5. Danerys being off from her character.
Daenerys after portraying the people choice of ruler from season 1 suddenly starts behaving like her father Madking. After the execution of missandei by the orders of Cersie to the mountain danerys attacks the kings landing in order to take back the iron throne but full of rage and anger against cersie she burned the whole city down from earth leaving just ashes all around. This was the most disappointing fact of season 8 that Daenerys burnt the whole kings landing from the ground.
All the fans are now waiting for the last episode of season 8 and really worried about what they will do without no Game of Thrones.