I've been thinking a lot about genre and pacing lately. In particular, the ways in which writers can play with genre and pacing. There are plenty of books out there about how to write a mystery, thriller, or romance. They talk about how to form the plot, how to pace the story, but there is something to be said for playing with these conventions.
Most genres have their own conventions, a certain way that plots unfold. If you are reading a mystery, it is a pretty safe bet that the first suspect they investigate is probably not the killer. Same goes for every police procedural out there. If there's 15 minutes left in the episode, you know they haven't caught the right guy. That said you can use the knowledge of this convention to twist readers' expectations.
Recently, I read The Alienist by Caleb Carr. The book is plotted largely like a thriller. There are no red herrings, they simply close in, drawing the noose ever tighter around the neck of the killer. That said, it's pacing was fairly even and it was quite a long book. There were several side plots that slowed down the main events of the story. I loved the book. It was creepy, atmospheric and kept my attention the entire time, but it's pacing was not what I expected. It moved a bit slower than anticipated, but it was that pace that allowed the extra time to get inside the killer's head, as well as into the heads of the protagonists. By going against my expectations, the book left me wondering what might happen next, what new revelations the team might make.
Pacing doesn't always need to match the genre you are writing, but if you do decide to take a different approach, it shouldn't be arbitrary. You shouldn't pace your story differently just for the sake of pacing it differently. Instead, it should serve a purpose. In The Alienist, the purpose was to allow the time to delve into the psychological concepts involved in building their psychological profile of the killer. This psychological profile is what sets the story apart and is the focus of the investigation, so it only makes sense to adjust the pacing to fit. However, making a story slow just to make it slow has no benefit unless you find a reason to make that pacing pay off.
To use the example of procedural shows, there are often episodes of cop dramas where the investigation is condensed, the pace quickened so that the killer is caught sooner in the episode. The episode doesn't end early, no there is always some kind of turn in the episode. Even though the killer is caught, there is some revelation: the killer has a partner, the last victim is alive out there, etc. The pacing of the story is specifically adjusted to make room for this turn. When done well, it can work brilliantly and leave viewers on the edges of their seats. It is all about knowing the story you want to tell.
So, while it is important to know that the standard conventions are for genre and pacing, that doesn't mean that you should be confined by them. Break the rules, but only when you have a good reason to. Pacing dictates how much tension there is in a story and how the reader experiences it, so choose wisely.