Curate, connect, and discover
Honestly, some fanfics seriously need "AU" or "ooc" markings, because some writers try to write about these characters, but in reality, it can be at best slightly, and at worst, very different from the original character, which, frankly, is often upsetting. And I understand that some writers can simply misunderstand/misinterpret these characters, but this is also a problem that would not exist if they wrote "AU/ooc" :(
And no negativity, I know a lot of writers do try and I do appreciate writers as much as any other artist (especially, as a writer and an artist myself), because it's a hard job and it takes creativity and skill (which you gain over time, all writers started somewhere and that's okay), but it's still bad writing if you're treating and selling these characters as "canon", but they're either very different or nothing like canon at all.
This is especially a problem for me when it comes from experienced writers and it's really sad that you see something that's well written and the conveyance of the characters' emotions, the characterization and writing, and the plot are great, but the fit with these specific characters is partially/completely zero and you're like "damn, I think they got this wrong". And again, this problem can be avoided by labeling it as "AU/ooc", especially if the writer likes their interpretation of the character more than the canon one. There's nothing wrong with liking a character's version better, you just have to accept that it's non-canon, that's all.
this is ultimately a personal preference but for me fanfiction hinges on correctly nailing the character's voice and mannerisms. When I say "they would not fucking say that" it's often not about the situation that's happening; it's about little tics and preferences and above all, diction. I'm not typically huge on AUs but I can be swayed if you nail the voice. and I am personally absolutely SHIT at writing plot, there's a reason my fic is pretty much entirely one-shots of emotional conversations, but you know what I can do is match a voice. and if you can do that as well I am along for the ride and if you can do that AND write plot you are a fucking genius and if you can't do that I'm clicking out of your fic the second people start talking.