Sometimes there's a paranormal romance series where there's a slow burn between the romantic leads, maybe with some misdirection along the way, and it takes until the end of the series for them to end up together (The Hollows, for instance). Sometimes there's one where they get together early, but they remain the leads (e.g. Mercy Thompson.) And then there's one like this, where they get together fairly early, and then, several books in, seemingly at random, the story just starts hopping around. Your former leads are now the old married couple, and there are new leads with each book, usually including one totally new character and one side character. ("Romance is catching" is kind of a trope in non-paranormal romance, too, for several reasons. Mostly, it sells books without a whole new cast having to be developed from scratch. That's fine.)

I can live with any of these, I guess. That third option does, of course, mean that the rest of the series will be uneven, depending how much you like the particular side character featured in each installment.

What I mind is when a series that is, admittedly, already a little dark and gritty suddenly goes all-in for "this character was raped and tortured for months on end and is deeply traumatized." That's ... not pleasant and is very much not my thing. I feel like there should be a strong warning on this book, given what a departure it is from the series so far.