It depends extremely hard on the artist. Since extreme fetishes are meant to give you back that feeling of inexperience and surreality you have when you get aroused for the first couple of times. Like, when you are child and experience Lust for the first time your thoughts, even if you know what´s going on is: "what the hell is this? And why do i like it so much? I want do dig deeper into this feeling". That´s what extreme fetishes are for me, if the art style is good in itself it will be arousing if you like it or not. That´s how you get into fetishes isn´t it? It´s for me at least, i like stuff nowadays i couldn´t imagine years ago just because one artist drew it in such a way that i couldn´t possibly be a downer. My problem with the extremely weird stuff like guro or scat is that 90% of art in that category is just.. shitty drawn and totally over the top. If you want to introduce such a fetish to an audience you gotta convince them step by step, page for page to hook them. If you just go "well, page 2? THE GURL IS AXPLOADING LULZ!" it feels to me the author rather drew it for himself then the reader.
To answer the question blundly,
No-go for me: scat, hard guro, bitter rape (the girl is not enyoing it at all or doesn´t succumb to it in the end), Netorare C (pretty much bitter rape, the girls never enjoys it)
Hard stuff i enjoy: Body Mods, Ryona, vore, soft guro (i dunno how to explain it)
Stuff where i go NUTS: Impregnation, Breeding, Cervix P., Netorare A/B (Girl succumbs to it in the end or wanted it from the start), Tomboys/Tomgirls
Since i red from some people here they don´t enjoy NTR, maybe i can give an explenation on my view on it. I think you only truly can enjoy this fetish if you know how to differentiate fact from fiction. For example, just because some people enjoy tentacles it doesn´t mean they want to get brutally taken by tentacles in every hole. A fetish in fictional work is, not a fantasy, it´s fiction. Just because i like it when people die in a movie because it get´s more dramatic i don´t enjoy it in real life. NTR is not about me wanting to happen that to anyone in real life, it´s because it´s forbidden fiction. It´s dirty and foremost not real. But that´s why i read books and watch movies, because sometimes you need to escape the real world and dip into something dark and forbidden, something you 'DON`T' want to be the real world. It´s stimulating and disturbing at the same time, it´s the whole "what is this and why do i enjoy it so much?"-feeling you can´t experience anymore. Like marmelade and peanutbutter on a sandwich.