I am not so much disappointed with the plot. Arya killing the Night King, Daenerys burning the city, Jon killing her and Bran becoming king is all fine but as you say it felt rushed. I think if they had just kept the format of 10 episodes for season 7 and 8 it would have made a big difference, allowing them to set up the events a little better.
RE: Game of Thrones Series Finale: 'The Iron Throne' Review