I'd like to talk about The Death and Life of Erza Scarlet a Bleach/FT fanfic. I read roughly to where they end the fake karakura arc/are in soul society dealing with clan politics.
At first, I liked it, Erza is a fun character to read, and it's interesting seeing her interact with the colorful cast of characters that Bleach provides. Ikkaku briefly being her mentor, her showdown/rivalry with Kenpachi, and her struggling to accept a world that's more unfair than her original is fun—lots of cool moments where other characters get the limelight. Anything with Kenpachi is great, seeing Grimmjow hijinks is fun, and it even has cool set pieces like Soul Society invading Hueco Mundo.
However, as I read the fic the more I got disappointed with it. The most obvious thing is its bad pacing. Well over one million words and I can't say it justifies it. The fights are slow, the character interactions are sluggish and the plot is lagging. I think this has to do with following Bleach's canon, not being sure where to take the story, and adding more characters than canon meaning it has worse pacing than the actual Bleach story.
The treatment for a lot of characters is bad whether it's extreme bashing/wanking. Mayuri in canon is a competent and strong soul reaper captain and has some of the most fun dialogue in the series. In this fanfic, he's a joke, a moron that gets bullied through the whole story. I don't know why the author hasn't bothered to kill him yet. They want the Quincy to get revenge on him but he's such a joke that it's pointless. Hell, I'm convinced a character like Komamura got killed so callously because in canon he beat the author's favorite character. On the other spectrum when the author loves a character they'll show it to you. Case in point Momo who I find annoyed more often than not. She makes other characters dumber when they interact with her, her last scene with Aizen was especially bad.
Finally, I think oftentimes the author attempts an idea but it immediately falls flat on its face. Like the espada. A lot of author notes highlight how they're gonna make the Espada way more threatening than in canon. In reality, they're more of a joke. Most of them are worse jobbers who get stomped to hell. Yama gets tortured by Byakuya, the other #10 Espada is there to show how cool Rukia is which is pointless because we see her run circles around Szayelaporro somehow. Stark beats a captain but it's undermined by the fact he immediately afterwards dies to Yamato effortlessly and Barragon's whole fight is just to show how cool Unohana is. The only ones who are seen as a legitimate threat are Tia Harribel only because she's the MC main fight meaning she has to be strong (although her living despite Erza seeing her murder Komamura is BS IMO), Nelliel, and maybe Ulquiorra. Hell even individual characters' plans are dropped. Chad is just worse here than in canon somehow.
I'm being very critical here but it's because of one main reason. A lot of the author notes highlight how one author likes parts of Bleach and the other author shows their disdain for most of Bleach. Saying it went downhill after Soul Society and especially became garbage past the Ulquiorra fight and how they could do better. The whole story has this sort of arrogance to it I feel where it's trying to state its the superior version to canon. Yet when I think of how Gin's death is dealt with in canon in comparison to this fanfic, Ulquiorra's character is much better in canon, how the authors don't like the rule of cool in Bleach yet will do it for characters they like, and a list of other reasons then I can't help but feel it's just done all worse.
I'm not saying fanfics have to be better than the actual canon story or that they have to be different/similar, etc. But the worst sin fanfic can do is constantly remind me of the original story. All I can think about now when I think about this story is, "Damn I wish I was reading the Bleach manga instead."