Let's say the story was introduced as a romance, then somewhere in the middle it becomes a horror/thriller, would you immediately think it's bad?
Would you feel like "This is not what I came here for, I came for the butterflies, not for this bull" would you drop the story/ get mad?
What are your thoughts on this style?
Do you think sufficient foreshadowing is necessary? Or is it fine to switch suddenly as long as the story remains interesting/ its executed well?
I think that without proper foreshadowing - even through the title or the cover - a story that changes genre in the middle will confuse, and probably anger most readers. If I was reading about the romantic conclusion of Charlie and Julia, and then suddenly a killer clown dropped through the window and killed Charlie, severely disfiguring Julia - I would probably not enjoy the book.
However, if you effectively foreshadow - mentioning a new "killer clown disease" and show that "Sweden has been quarantined from the world" and then show the clowns invading a nightclub, so Charlie and Julia can fight the incoming foes, and then die in a beautiful death scene finally admitting their love for one another - in other words if The romance doesn't stop because of the thriller or horror, I think that most readers would enjoy, or at least not totally hate the concept.
So in summary, if you change the genre without foreshadowing, or continuing the subplot - if Charlie and Julia's lovely supper becomes a murderous chase, where Charlie goes insane from grief... Then I would hate the book. But if you show a well-established relationship continuing in the face of adversity, that may be a great plot idea - for great examples of this read many YA books (e.g. Divergent, or any-paranornmal-romance stories). Warning - lots of this kind of book are NSFW
Genre is a contract you make with the audience. If the genre is action/adventure, you're promising the audience that there will be an action sequence to resolve the plot. If its horror, you're promising that the ending will be terrifying. If it's romance, you're promising love. Comedy...laughs.
If you change the genre partway through a story, you're breaking a promise. It's bait and switch. Your audience will be angry and disappointed.
Of course, it is possible to combine genres, but you have to understand what you're promising the reader, and you have to fulfill the contract: give them what you promised.
Every book begins by creating expectations for the reader. The expectations start with the cover and title, and are built throughout the beginning of the book. If readers do not feel that the book satisfied their expectations, they will find it disappointing.
To illustrate why your idea, as described, is likely to fail, here are some example readers.
Harry loves romance, but hates horror. They were very excited when they saw your book, and immediately began to read it. Upon getting to the twist they dropped it and walked away. Now they refuse to read anything by you, and will encourage all their friends to avoid your books.
Jessica loves horror, but hates romance. They took one look at your book and walked away. They have no interest in reading a fluffy romance, and they'll never get far enough into it to find out they would have liked the book.
Chris loves romance and horror. They saw your book and added it to their "fluffy reading" stack, to save for a nice comfy read some time in the future when they were having a bad day. When they got around to reading it, they were unprepared for the horror and had to put it down. They might have liked the book under other circumstances, but now they associate it with the distress they were feeling that day, and can't finish it.
Alex loves horror and likes romance. They were warned ahead of time about the twist in your book and therefore picked it up eagerly. However, the twist fell flat for them because they knew it was coming, and they only found the book to be mediocre because of it.
Jordan likes horror and romance. They found your book without forewarning, enjoyed the twist, and thinks that this is the greatest book ever written. I guess 1 out of 5 isn't bad?
It's really only 1 out of 4, because Harry was never going to like your book. And of course your potential readership can't be neatly and evenly split between Jessica, Chris, Alex, and Jordan. But I think you see my point. There are a number of ways in which hiding your true genre has the potential to alienate your readership, which is something you absolutely want to avoid.
For further reading, I recommend Fulfilling the Reader's Fantasies on the Writing Excuses Podcast.
A discussion on fulfilling the promises we make to our readers—specifically the genre-specific promises made by the simple fact of where the book is shelved.
I don't think that I would be "angry", but I might well be annoyed. If I'm in the mood to read, say, an action/adventure story, and I pick up this book thinking it's going to be a lot of violence and action, and then after the first chapter it turns into a sweet and pleasant romance ... well, that's not what I wanted to read. Even if I like romance novels, maybe that just isn't what I wanted to read today. It would be like if I decided I wanted an ice cream cone, went to an ice cream parlor and ordered an ice cream cone, and it turned out to really be mashed potatoes. I like mashed potatoes, but that's not what I wanted right now.
I could especially see this being an issue in your case: shifting from a pleasant story of love and romance to a graphic horror story. That is almost surely not what the reader was looking for. She wants romantic escapist fare, and suddenly there is blood and gore and hacked up body parts? Even if you're not contemplating being that graphic, this is a problem.
It would also be difficult to make the transition while keeping the story coherent. Not impossible, of course, but tricky. You spend the first few chapters building up the heroine as beautiful and desirable and the hero as rich and handsome or whatever ... and then suddenly all of that is irrelevant and what matters is their ability to fight off a chain-saw wielding maniac.
Now I haven't read your story. Maybe if I read it I'd say, "Wow, that's cool the way he smoothly shifted from a romance to a horror story. It all flowed so naturally and made so much sense that I'm not even sure where the transition really happened."
But really ... probably not.
I personally am not into romance. I prefer horror over it. Others feel the same way; others feel the opposite. Some like both.
As long as you do a smooth transition and it works well, you should be fine. Also, if you want more readers, I suggest keeping down the romance some. Women prefer romance over men a huge amount. Men prefer horror over women. Just keep the romance down, and make it realistic.
