The Book Which Should Not Be Named has been referred to numerous times as a supremely bad first book in a supremely bad series. Its mimics, too (and there are so many in YA and in both straight and LGBTQ paranormal romance that I can't even list them all), have been amazingly bad. Nevertheless, I think the concept could work--could, in fact, be interesting!--if authors would do one thing:
Write the supernatural-human pairing as horror.
This allows you to write the male protagonist as the psychopathic, emotionally abusive control freak-predator that he is. (I'm not speaking of any particular character; sadly, the vast majority of the male protagonists that I've seen in paranormals and romantic fantasy fit this description.) You'd have a supernatural predator hunting for naive and susceptible humans in settings where he seemed to be perfectly normal--getting them to trust him and to be willing to give up their families, their friends and their lives for a guy that they think they know. He could claim to be harmless and not a predator at all. He could even make this claim plausible. But of course it would all be lies. It would be very clear to the reader (if not at all clear to the other protagonist) that this guy is bad, is using her and is trying to lure her in.***
Or, conversely, it could allow you to write the female protagonist as a lying, pretentious, arrogant, manipulative sociopath who falls for a supernatural being and who is determined to acquire inhuman beauty and immortality. And she'd stalk this being around the world until she got what she wanted. Even after she got what she wanted, because she'd feel that she was his equal then, and that he should love her and her alone. (Three words:
Kiri, kiri, kiri!)
Or you write a story in which you know (and consequently the narrative of the story knows) that they're both horrible, selfish monsters--one human, one not--who hurt those around them. Bonus points if people see that they're horrible and react to it in various ways. Because then you have conflict. And conflict moves the plot, develops the characters and, ultimately, makes the story.
The main problem with the novels that I've mentioned is that the writers are attempting to meld the romance trope of the sullen-yet-fundamentally-good Byronic hero with that of a monster protagonist. This is a bad move, because it effectively neuters the monster and kills off a ton of conflict and suspense in the process. It also often sends a decidedly anti-human message, in which the human protagonist is all too eager to shuck off "inferior" humanity for the sake of becoming something stronger, faster, smarter, longer-lived and more beautiful than any human could ever hope to be. And because the monster has been rendered harmless, the authors of such books tend to downplay any weaknesses or problems connected with being a monster...if indeed such difficulties exist at all.
Instead, let the monster be a monster. Not nice. Not harmless. Not a broody angstmuffin. Let him or her be the predator, the psychopathic killer, the cannibalistic threat that the authors of such books keep insisting that creatures of his or her species (vampires, demons, shapeshifters, fallen angels, fae, etc.) actually are.
If the author lets herself be aware that the monster IS a monster, there's more of a plot. The monster can still be creepy and stalkerish and obsessive, but the narrative doesn't pretend that these are elements of a relationship that should be encouraged. The monster can still pretend to be kind and charming...but that's just to get the prey closer. The human protagonist can be in love with the monster, but that is far from being a good situation; instead, love becomes both a trap and a weapon. The human in the equation actually IS in danger--and, being one of the protagonists, will eventually have to do something about the bad situation he or she is in. There's tension, suspense and an actual problem that needs to be resolved. All of which would be a lot better than this:
Human: I love you.
Supernatural Being: I love you, too, but we can't possibly be together.
Human: But Supernatural Being! I'm willing to give up my family, my friends, my future, my dreams, any chance of a normal life, my biological life and my soul for you, even though I just met you five minutes ago! Doesn't that solve all of our problems?
*cue artificially engineered breakups*
*ANGST ANGST ANGST*
*minor injury to human protagonist, which he or she suffered to tell us that a danger to him/her was real, despite the fact that NO protagonist in the romance genre ever gets killed off, as that would ruin the happy ending*
Human: I still love you.
Supernatural Being: I love you, too.
*insert romantic scene to convince readers that the situation has changed from what it was in the beginning when, in fact, it has not*
THE END
***(Interestingly, most gay paranormals have the two male protagonists on an even keel--two shifters of different types, an older and a younger vampire, and so on. Even if one of the male protagonists is human, he doesn't remain so for long and is never powerless compared to the older monster. It's generally in the het romances that you find the powerless human girl or woman and the vastly superior male supernatural being. Completely different dynamic.)