This story was a classic revenge tale! This tale could have been told in any world, and I think for most fans, the disappointment stems from "it didn't have to be _THIS_ world"! The world constructed by the authors of the previous game had so many facets that could have been further explored, but instead, we got (what I believe to be) a reasonably generic revenge story.
Sure, both sides had their reasons for revenge, but that misses the point, this game is about the apocalypse caused by a deadly disease. At what point did the disease have any level of salience in this game? Ellie wanting her life to mean something felt like an after thought. The reasons for Ellie and Joel's patchy relationship could have been substituted for literally anything else. The reason Joel killed Abby's dad could have also been substituted for literally anything else, and I could continue to go on here.
I agree that the characters developed here. I agree that the story was fine (I hesitate to call it "good"). But I'm upset because I don't think it belonged in the world of the last of us. Most of the criticisms that the developers are facing essentially stem from that simple fact. This game, and this story had a right to exist, but they should not have existed in the world of the last of us. That is ultimately how I feel about this game.