Without a doubt, one of the most heartbreaking moments of The Last of Us 2 is Joel's death. He's a fan-favored character who goes from cold-heart smuggler with a tragic past to love father figure to Ellie. All of that is stolen from him at the beginning of The Last of Us 2, of course, but many would agree the measure of a man is often what he leaves behind.
The Last of Us 2's Joel is a man who left behind a lot, and in looking at how he made the world around him better, it's even clearer as to why his death spurns such hatred. There's many who want revenge, not just Ellie, and it's clear why: this revenge is the type born out of the one thing, love.
Joel and Ellie
Obviously, the most important relationship is that between Joel and Ellie. When he was delivering her to the Fireflies in The Last of Us, the two grew close together, eventually forming a father-daughter relationship. After losing Sarah, Joel was hardened and cold, but Ellie brought him back without forgetting Sarah either. This somewhat soured by the beginning of The Last of Us 2, as Ellie discovers what Joel did to save her life, but Ellie says that she wants to try and forgive him.
In those memories, players see how Joel is pushing Ellie to pursue Dinah and to live life. He encourages her, in so many words, to stop thinking of herself as some sacrificial lamb for the world, and as her own person. At the end of The Last of Us 2, Ellie tries to play guitar but realizes she cannot because of the damage down to her hand, a lesson that Joel also tried to provide—that his former lifestyle takes, it doesn't give. Whether she learns this lesson, as encapsulated by this scene, is entirely up to player interpretation.
Joel and Tommy
In the original game, fans learn over the falling out of Joel and Tommy in the first game likely due to how Joel lost himself in surviving. Tommy joins the fireflies to try to make things better, but Tommy claims that he still has nightmares from those days. However, by The Last of Us 2, it's clear the two have more than made up. The relationship between brothers is clearly formed on mutual respect and love, so much so that Tommy is initially more persistent in the pursuit of Abby than Ellie. Losing Joel and then his eye is no doubt a hardship on Tommy, potentially making him regress in his ways.
Ultimately, it's uncertain how a threequel in The Last of Us 3 would expand this story, but if it were to, then Tommy is likely a different person for better or worse, having also separated from Maria (likely as a result of his own trauma). This would be especially true when he learns that Ellie let Abby live, and those changes may not be good. They would still be a result of the love Tommy had for Joel, and what Joel left behind. Before finding Tommy in the first game, Joel remarks that Tommy's last words to him were that he did not want to see him ever again. Now, it's clear that Tommy would do anything for that one chance.
Joel and Jackson
Of course, it's not all about the big relationships. Joel left behind Jackson, a town he had come to love and a town he would be willing to die to defend. It's clear that he and Maria had become close, like family. It's clear that Dinah and Jesse had the upmost respect, and while Joel does have normal, everyday conflicts in the town, many looked up to him.
Joel's death is a tragic event, one that every character in The Last of Us 2 has to learn to live with, to move past, or become mired in. While hopefully Ellie has learned to move past, Tommy may not have yet. Many in the town may not have yet, and that's the heartbreaking truth: he changed those around him, as much as Ellie changed him.
The Last of Us 2 is out now on PS4.