Bittersweet. While the protagonists eventually manage to stop the antagonist's plans, it's not without a lot of casualties and the implication they did more harm than good.
The original webserial version of the story had jumpscares embedded in the page, but it's not in any modern digital copies. Unless your book is possessed you've got nothing to worry about now.
I don't know who moderates this site but I feel I should stress that yes, that is the actual book title, and yes, it really does have quite a lot of spider-like monsters in it.
Several parasites are burned alive. The corpses of infected individuals are thrown into a bonfire, with the smell of flesh and the sight of bones described repeatedly throughout the book.
A character is restrained by a police officer in dangerous proximity of invisible parasites, and is only released after one starts eating him. Several other instances of characters being arrested by authorities, and one instance of a character waking up handcuffed to a bed with no memory of how they got there.
Dave (the narrator) is required to attend court-mandated therapy sessions in the early chapters of the book. Several scenes in an asylum that has been refitted as part of a emergency quarantine zone.
While far from the first death in the entire book, TJ is the first to go in the Ffirth Asylum Massacre despite joking about it mere minutes beforehand.
Prior to the events of the book, a female character is stalked by someone (or something) impersonating a pizza delivery man. He eventually breaks into her room and is chased off and possibly shot by her partner. The Narrator also offhandedly remarks that he is frequently stalked by amateur paranormal investigators.
John's alcoholic tendencies get much worse following the outbreak (and what he assumes is Dave's death), leading to a week-long bender that fractures his friendship with Amy.
As per usual for the series, if someone gets in a car they're probably not getting out until it's crashed or at the bottom of a lake (with them in it). A character also falls off a motorbike, but he's unharmed.
This book is basically a zombie apocalypse story, but with spider-parasites instead of a typical infection. The initial outbreak occurs at a hospital, much of the action takes place in quarantine zones, and at one point a protagonist wakes up handcuffed to a medical bed.
The book is written under the pretense that David, a main character, is the author and is talking about his life. He writes in a fairly conversational tone but never really breaks the fourth wall. (At least not beyond telling readers of the first book to go fuck themselves.)
Fairly early in the book, a character recalls a paranormal experience they had while they were taking a shower. The entire segment is written in italics and can be skipped by looking for the next non-italicized part.