The last two books weren't just useless back story.
All of the stuff with Jon at the wall. Everything with Arya in Braavos. Cersei's downfall. Jaime's character turn. Reek. Victarion being insane.
People get pissed because a lot of the plots were disappointing: Dany, Brienne and the Dornish stuff. But people should remember how great some of the other stuff was.