Lately, I've had a recurring rant that Brian's had to listen to several times. It's the topic that comes up in the pool, when we're on the couch or when we're driving to the store.
You can use several terms to refer to the topic. Atmosphere. Tone. Ambiance.
I'll use tone.
The emotional response of the audience says a lot about the tone you've created. Consider Breaking Bad. Consider just the simple act of closing a garage door and the "Oh shit" response that's out of your mouth before you can even think. That's a gut-level response to a show that continuously takes a bad situation and makes it worse. A show that twists in directions you don't see coming, and don't want to see coming, but like a train wreck in motion, you can't stop watching.
A lot of people seem to have issues surrounding genre, and figuring out where their book fits.
If you've written a book where the cat is flung out of the window and ends up in a dumpster after using all 9 lives, you haven't written a cat mystery. I'm thinking a little more hardboiled/noir.
If you've written a book where, at the end of every chapter, the problem's been solved and everything's okay, it's a little more likely that you've written a cozy. You know, cozy. Makes you feel warm and good at the end.
If you've written a book where every avenue of investigation leads your cops into more danger, lives are at stake, there's a deadline fast approaching and failing to catch the bad guy in time will result in your protagonist losing what's most important to them (or central to the story) you've probably written a thriller.
If you're the audience, and the female lead is continuously rescued by one guy or another, and all she really thinks about is how she feels about a guy, you aren't generating a sense of dread or building a tension about imminent threat. You've written a romance.
If you want a good case study, watch The Lion, The Witch and The Wardrobe, and then watch LOTR The Two Towers. One movie has scene after scene resolved with upbeat music and happy smiles from kids who can still be kids. The other has the overwhelming sense of imminent death hanging over everyone. Sure, both stories apparently have a central character who comes back from the dead, but in one, he's jumping around and playing with the girls. In the other, he looks like hell and barely makes it in time to warn the others of the massive army coming to kill them all.
In just a few hours of watching those movies, you can learn more about tone and the effect on the audience than I could effectively share in one post. People run into problems when they want their book to be one thing, but can't maintain the tone needed for that effect. In LOTR, the banter between Gimli and Legalos is essential for breaking the tension because of how dark and how overwhelming the sense of dread is throughout. Watch that scene above, and note how the quiet is used, how weather is used, how every element works together to put you on the edge of your seat, waiting to see what will happen. The fear is palpable.
And people run into problems when 99% of the book has a certain tone, and in the end they shift gears wildly, hoping for a dramatic finish, that doesn't fit with the tone of the rest of the book.
Know what you want your story to be, and don't be ashamed of that. Make it what you intend... don't let the fear of landing the punches keep you from giving your story the edge you're after.