In some ways, this comes off as two different novels combined into one. The first novel is a story about Oasis, a young woman who nearly died as a cult member, learning to love, trust, and reconnect with both other people and reality itself in the aftermath of that trauma. She also struggles to overcome shame over having gotten sucked into the cult in the first place, over having left the other cult members behind to suffer and possibly die, and over the extensive scarring cult rituals left on her body. This plotline is grounded in psychological realism and a keen understanding of cult dynamics; the imagined cult isn't obviously based on one specific real cult in particular, but its bizarre, disturbing practices and theology contain elements of everything from Heaven's Gate to Jonestown to the various groups formed by notorious internet con man Andy Blake.
The second novel is a lighthearted and absolutely bonkers wish-fulfillment romance about Oasis, a young woman who meets and immediately falls in intense mutual love with Count Dracula, immortal vampire and genderbending shapeshifter, currently manifesting herself as a gorgeous twenty-four year old Black woman named Laura. (This Dracula plays by quasi-Carmilla vampire name rules: s/he doesn't have to use every letter of "Dracula" when s/he chooses a new name, but the name does have to be made of letters that are in "Dracula". Hence, s/he's been Darla, Al, Raul, Carl, etc.) Although Dracula/Laura is being pursued by the descendants of Van Helsing, Dr. Seward, &c., this threat and its eventual resolution take a backseat to Oasis's various supernaturally-inflected dates and encounters with her new girlfriend, whose personality and mannerisms are sort of half Gary Oldman's version of the Count in Frances Ford Coppola's 1992 film adaptation, half Nandor the Relentless from What We Do In the Shadows. There's a vampire bunny and a vampire kitty! Being Dracula's girlfriend means you get access to all kinds of opulent luxury! Also, you get to see Dracula turn into bats and stuff! Since she's hundreds of years old and has had countless partners, she's amazing at sex! Laura and Oasis visit a vampire/werewolf/revenant nightclub!!
The vampires and werewolves do kill and eat and torture people, but it's treated very lightly (again, think What We Do In the Shadows). The people who get tortured are usually pedophiles or murderous cult leaders or something along those lines. The people who just get eaten are never named characters. Only the *really bad* supernatural creatures, the ones you're not supposed to like at all, would ever stoop to sexual assault.
You might already have noticed two potential problems here-- problems which, in my opinion, DARKNESSES never quite manages to reconcile, although it tries very hard in its final third and does manage satisfying, complete-feeling resolutions to both of the novels that it is.
The first problem is that the gravity and realism with which the first novel treats the many abuses and transgressions of Zeke, the cult leader, and the PTSD Oasis suffers as a result, can ring a little hollow (or at least seem very odd) when juxtaposed with the cheerfully amoral, handwave-y treatment of Dracula & friends' killing and torturing all over the place in the second novel. I mean, sure, most of them need human blood to survive, but it's established that they can get that *without* killing anyone (and certainly without having fun killing people in drawn-out ways). When the reader is immersed in that plotline, it's easy to roll with it because the vampires etc. are likable and only rarely come off as malicious: their killing for pleasure is catlike, the behavior of a literally different, predatory species. Also, it happens almost entirely "offscreen". But when we're brought back to the first plotline, and we're suddenly supposed to be taking Zeke's comparatively small potatoes murders, assaults, and torture extremely seriously, the way we would in real life, it's jarring.
The second problem is that, for a character who is in recovery from cult brainwashing by a group that persuades its adherents of supernatural nonsense, Oasis just isn't very conflicted at all about going out with a woman who says up front that she's a vampire and comes on super strong in a way that could easily read as love-bombing. While Oasis does *acknowledge* that it's odd she's not more suspicious, doesn't see certain things as red flags, etc., I couldn't help but feel this should have been a way, way bigger point of uncertainty and drama in the early stages of the romance-- I think it would've added a lot, as the entry into a relationship does feel rushed (as previously mentioned, it's literally love at first sight!) and early scenes of Laura having to more actively court Oasis, figure out how to approach her in ways that don't activate her trauma, and persuade her she isn't a threat would have been a neat parallel to later scenes of Oasis trying to convince Laura to let her guard down and trust enough to drink Oasis's blood (it's a whole thing, not going to explain it here, this book is for you if "horny human begs reluctant vampire to drink from them" is a dynamic that revs your engine).