Taking your asking about light or web novels.
I never keep any thrilling expectations on these actually, it's just a fun side snacks from the deep&heavy novels.
So, what really ticks me off will be those with narrow plot lines - CN novels where there's no room for any actual story other than masochism and cultivation, I don't mean the ones with subtle masochism, but those that just defies logic.
Amateur comedy, it's just awkward sometimes to read what meant to be a joke but just doesn't suit the flow of plot.
Harem- till now I've never read any decent harems. It's alright though, it's actually comical for me seeing how mc plucks fl's like fruits from tree. Don't even get me started how they never have any individualism, or opinions of there own. XD ok the last one isn't comical, but it's just become norm for me in CN now.
Plot Armor- I get it, it's all about how destiny chose him/her to be savior of this xxx world, but just face-slapping us with " mc can't be F**ked" with no consideration to creating depths, and interesting plots, you never for a sec even get to imagine of this mc ever being in mortal danger.
well I guess I really do take it all seriously XD, it's just I can't help being opinionated when reading.
But I consider light novels to be like written soap opras, with writers looking into quantity over quality, so it's f9.
I've mostly read CN novels so I'm not sure how the jp, KR works out.