The positive reception to the ending is hard carried by the fans' previous knowledge of Henry from outside material like the silver eyes novel and matpat talking about said novel.
Henry is not a fucking character in the games, he's never mentioned directly, introduced or developed in any meaningful way. He's a non entity. He didn't exist in the games. I used to like the ending until a friend on discord blackpilled me on how the only reason I like it is because of outside knowledge of the character from a book that is not even in the same universe as the games and not because of the merits of the writing of the ending and game itself.
I mean ask yourself, if you never read the novel and you played the games in order, how will you react to the ending ? The answer is you'll be completely confused on who this random faggot is who showed up out of nowhere, killed everyone, had a gay monologue about how william was mean to him and then fucked off. Nigga who are you ? Where tf were you in both the games and in game lore in the past 30 years and wtf were you doing and why were you never mentioned at all ???? The game deadass acts as if we knew this character since fnaf1 and we're supposed to be rooting for Mr.literally who coming out of thin air in what's essentially the last 5 minutes of the story and becoming "the hero" by executing all the named characters. Who invited bro ?

bro thinks he's part of the team
Scott said that the novels aren't meant to fit with the games but bends backwards and makes the ENDING of the series reliant completely on a character he borrowed from the books and slapped on the games in the last 5 seconds. He's not even called Henry in game, he's fucking "cassette man" game literally isn't hiding the fact that it doesn't even wanna try to give him any semblance of comptent character writing and development because "aah whatever, they prolly read the novel or watched matpat talking about him". He's a textbook example of Deus Ex machina summoned by Scott from a different universe to just get rid of a bunch of characters that he doesn't know wtf to do with them in the lore. Nigga that ending is dogshit and needs to be mocked more