Yet again, I'm trying to organize my own thoughts by recording them - talking about what I avoid to understand why it bothers me. Not terribly interesting, but it does help me think.
As I've said, I love fanfiction. My opinion on it - on all media, really - is that the execution matters far more than the idea. Anything can be done well, and anything poorly. That doesn't make concepts irrelevant - the more far-fetched an idea, the harder it is to write credibly - but it does make them secondary.
For this reason, I will read just about anything, because anything can be good. However, there are a few things that are very hard to do well, and I generally avoid these. I've read them all when the story was good enough, though.
Porn: Fairly obvious. I read for the story, and reading about sex generally doesn't do much for me. I do read stories with explicit sex because to ignore it would be to miss out on a lot of the genuinely good stories. Many of the writers who are mature enough to write well are mature enough to want to read and write sex scenes, and that's absolutely fine. But since I read for character, I don't usually enjoy stories that are purely sex. Lots of sex is fine, if it's well-written and there's a good plot in there somewhere -
The Cure for Boredom comes to mind. The entire story revolves around sex, but it's also well-written, in-character, and surprisingly enjoyable. My problem is more with the presence or absence of a point - and the quality of the writing, because sex scenes are easy things to ruin - than the sex itself.
BDSM, or other kink: Pretty much the same as porn, but slightly worse because much of it isn't my kink, and while I respect people's right to read and write these stories, if I don't understand the appeal, then it's hard to understand the story. Sometimes there are also consent issues, which makes it worse. I have no problem with BDSM sex or romance if it's written well- I loved the Kushiel's Legacy books. I'm also quite intrigued by the idea of absolute trust that's part of any decent BDSM, but half of what's out there is porn and three-quarters is poorly-researched and worse-realized. As such, I tend not to seek it out.
Eldritch Horrors'
The Cold Song is a beautiful counterexample. It's half porn, but the sex is all actually important to the plot and characterization, there's an excellent plot, and the author - a former pro dom - actually knows what she's talking about with regards to BDSM.
Noncon and Dubcon: I value choice above almost everything else, so noncon is abhorrent to me. Even if it's portrayed as negative, it's painful, and I really don't want to read about rape or torture. If it's positively portrayed, then I try to forget its existence. I really don't want to understand how people see that as attractive. Dubcon I will read if it's well written and not blatantly coercive, but it's still a bit squicky.
Blind Author's
Reaction does noncon painfully well, especially since it makes no attempt to be sexy, and is instead works very effectively with characterization and recovery. Still not my cup of tea, but very well-written.
Omegaverse (or Sentinel/Guide, or dom/sub - they're a similar category): It's mostly porn, with extra dubcon/noncon, stupid, outdated gender politics, and terrible biology. Occasionally an author manages to focus on the characters and treat it as another AU, and then it's interesting, but mostly it's an excuse for bad porn.
However, fresne's
Phrygian Choices is an awesome exploration of sexuality and gender through the lens of Omegaverse, and it's absolutely amazing.
Terrible pairings: I don't generally actively ship noncanon pairings, but I'll read most anything if the author can write it credibly, because good writing can make a lot of things believable. The only ones I don't read are those I abhor. Any incest falls into this category, as do things like Buffy/Giles and Snape/Harry. Of course, if I've read it done well enough, then I often no longer see it as quite that strange. Which is why I tend to avoid pairings I really can't stand - I don't want to see them as credible.
Nicolette Says Jump is a really weird combination - Xander/Spike/OC Female - done surprisingly well. It's a one night stand rather than a romance, and drugs are involved, but it still works better than it has any right to.
Fandoms I don't follow: Pretty obvious. I have a handful of works that I love, and those are mostly what I look for. I make exceptions for great writing if I'm passingly familiar or even unfamiliar with the source material - especially if it's a crossover and I know the other half - but why read about characters I don't care about?
I made an exception for
Sleeping With the Girls. It breaks lots of rules, actually. Sleeping With the Girls is an anime multicrossover self-insert in which our main character, who still has not been given a name, discovers that he wakes up in the bed of a different anime girl - always one of his favorite characters - every time he goes to sleep. Despite the premise, there is as yet no sex whatsoever. The SI likes tsunderes - most of them have tried to kill him, and the story is about him learning to survive and completely screwing up most of their worlds. This is how to do a self-insert right: honestly, so that the character is a flawed, interesting human, not a perfect, boring Mary Sue. I read it to see self-insert done properly, and figured out fandoms as I went because the writing's entirely worth it.
OOC, to an extent: I should note that I consider AU versions of a character different from OOC. If X has a different life story, then it's fine that she's a different person. If you're going to do a different version of the character, then do it consistently, and show how they change - like
Methods of Rationality. Harry there is NOT canon Harry, but he's awesome nonetheless. Reinterpretation is also fine to an extent because there is a difference between defining a character based on what they've done, and ignoring what they've done to make them who you want them to be. Severus Snape can be written as an evil Death Eater, as a deeply unpleasant but not evil man whose only redeeming quality (if it can be called that) is an obsessive loyalty to a woman long dead, or even as a good (if inhibited, abrasive, and deeply flawed) man who has spent his life trying to find redemption for the mistakes of his youth. If you're good you can keep Snape in character and make any of those descriptions work. What you can't do is have him break into tears in the Great Hall, or run from behind his desk to embrace Harry on his first day - at least, not without significant provocation and a very good explanation. If you're going to have a character do something that seems unlike them, then you'd best have a very good reason and write it very, very well. That goes double for shipping, since you can't actually reverse a character's personality to make your OTP work - not that far too many people don't try that.
I love to see a different take on a familiar character - all fic does that to some extent - but they do have to remain themselves, rather than being same-named OCs.
Skeleton Key plays with this idea - most of the story is devoted to explaining one seemingly OOC action, and it's brilliant.
RPF - I like meta quite a lot, if it's done well, but I find RPF rather odd. It seems strange to play with real, living people as characters, especially if you're writing about their sex lives. On the other hand, historical fiction is a valid genre, not to mention urban legends and gossip. Or the entire mythos that's grown up around Chuck Norris. For that matter, history itself is to some extent a matter of interpretation, and it can be hard to filter out the real truth of someone's life. As strange as it seems to reimagine the lives of people who actually exist, we seem to do it constantly, so I find it difficult to object. That said, I also don't care about most celebrities nearly as much as I do about fictional characters, so I mostly don't bother to seek out RPF. Exceptions, as always, are made for exceptional writing, especially if I like the author.
Besides,
this exists, and it amuses me.
That's really it. Many of my hangups are sexual, which I already knew, and for the most part my problems have more to do with certain concepts being very hard to do well than with the concepts themselves.
I will read AU, crossover, kidfic, sickfic, crack, angst, adventure, romance (het, slash, or femslash), and just about anything else if it's done well enough to make me want to believe it. In fact, I don't see any problem with some of the things that are often seen as problematic, like OCs. The main things I look for are quality and internal consistency - if you want to change the rules, then be consistent about it and do it well. That's what stories are for - all of the rules are only guidelines, and all of the really good stuff stretches the limits.