I think we all have "rules" about what we do or don't like to see in a book. No children/secret babies/virgin widows/ridiculous misunderstandings/whatever. I may have more rules than most people and I can be very stubborn (ask anyone who knows me). In general, I think we're right to dismiss a book others love because it has elements we think won't work for us. But every once in a while you'll come across a book that is the exception. And you see that in the hands of the right author you can love what you profess to hate.
Here are some of my rules that have been broken lately. (And yes, massive generalizations here. Don't judge. I'm growing.)
Alphas are assholes. Tonight I finished Heyer's Devil's Cub and the hero was really Alpha--domineering, aggressive, with a wretched temper and very little kindness. By all experience, I should have hated him. Oh, no, no, no! I LOVE Vidal!! (Gushing review to come soon.)
Science fiction is weird and boring. Bujold's Vorkosigan series and Linnea Sinclair's books have spaceships, laser guns, alien life forms ... and completely awesome characters, and totally relatable storylines.
Vampires are super gross and should not be heroes. Colin in Meljean Brook's Demon Moon--he drinks blood (ewww!), and he gets off doing it (double ewww!). He's also smart, really funny, and god-damn sexy. I lurve him (though I still don't think I'd let him bite me).
Ghost stories are creepy and not in a good way. I don't usually like the brooding, gothic, chillingly shivery kind of book. And ghost stories scare me more than I'd care to admit. The Shadowy Horses by Susanna Kearsley is my exception here. And I don't even love this book despite the ghost story---it's actually one of my favorite things about it. It's a pretty tame ghost story, but still.
I'm becoming more open-minded all the time. :)