The whole game is about obsession and how it ruins one's life. Neil Druckmann himself compares it to drug addiction. Abby obsesses over finding and killing Joel to the point of not being able to live in the moment at all, resulting in her losing everything she cares for. Owen has moved on, and Abby has turned her body into a machine just for killing Joel, but even that does not give her the satisfaction she thought she would have. she still has constant nightmares about her dad's death. Ellie essentially goes through the exact same storyline of hunting down the father's killer, except Abby's story is further along. Ellie also loses everything she cares about because of her obsession. At the farm house, we think she will have a happy life but that simply is not the world of the last of us. Ellie is haunted by Joel's death, and is only pretending to be happy there. In this part of the game she keeps having flashes of Joel's death. However as she is about to drown Abby, she finally has a flash of a happy memory of Joel. She has finally moved on and is able to let go. She has to end the cycle of violence or it will only result in Lev coming after her. However when she goes back to the farm, she realizes that this obsession really did take everything from her. She has even lost her fingers, unable to play the guitar the one happy thing she has left of Joel. We think the farm scene, and the fight was the last thing she said to Joel before he died, but in the final porch flashback we learn that she was going to finally start to try to forgive Joel (according to Neil Druckmann the movie night Ellie talks about in the beginning of the game would have been the first time they really hung out in years) but that opportunity is taken from her. This revelation makes Ellie's inability to let go make sense. Through forgiving Abby in the end, she finally manages to forgive Joel as well, tying everything back to the ending of the original. I thought the ending was absolutely masterfully done and it affected me very deeply. I hope you can understand my perspective and why I don't like it when people oversimplify this narrative saying the ending sucked. Thematically it fits perfectly in my opinion. While I still like the original better, I think this game is also nothing short of a masterpiece.  

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I think the ending is so powerful. Abby's story mirrors Ellie's so well, literally hunted down her fathers killer for revenge, but she doesn't get the resolution she was hoping for. She tries to redeem herself, move on and through her connection with Lev she realizes that revenge is not the way, not killing Dina and Ellie at the theatre to set the right example for Lev. Ellie however cannot move on, and keep chasing this fantasy of a revenge and ultimately ends up losing everything. We see in the end that Joel and Ellie were just aboutnto try to memd their relationship, when that gets taken away from her and she just can't accept a normal happy life knowing how she could have been the cure. In the end in hopes of making amends she loses the good part of her connection to Joel too, literally symbolized by her losing her fingers and the ability to play the guitar, which has been a pivotal plot point throughout the game so far, especially in the good memories of Joel. I still like the narrative of the 1st one better, but saying this game is not well written is completely insane imo.