It started well, reminded me of my first forays in m/m when I read vampire slash fanfiction and I liked the first half. I thought that the story tended to derail when it tried too hard to be dark or went off on tangents, I found that Nicholas was an exceptionnally bland, almost non-existant character, but I didn't mind too much. It was Ban's story and it suited me just fine because I found/imagined some interesting threads I couldn't wait for the author to develop. Which she didn't. But keeping on trying hard to be dark and shocking, going off on tangents she did.
The result is that the premises of several potentially great stories are co-existing in this book and never connected with each others to go beyond the status of premises. To name only a few :
This question in particular is at the core of the story and it is highly ironic that Nicholas is such an under-developped character. I don't like the reincarnation/fated mates trope, but it would have been very interesting to follow this character, recognize the fundamental traits of his being through his successive lives and understand that it was with this being that Ban was in love with. Instead, the clue to recognize Nicholas is to count his balls!
I will not elaborate about what went wrong with Ban, but none of what could have been interesting has been developped and in the end, this story is fluff with special effects, relying a lot on shock value to be dark. Which leads me to wonder what the word 'darkness' actually means : surely, it's something different from a build-up of gory and rapey details! Mind you, I don't have any final definition to give but it would have something to do with loss perhaps : loss of hope, of boundaries, loss of self... For me, darkness lies in someone's soul and it's when it reveals itself from something apparently trivial that it is chilling.
If you are actually interested in vampire stories with no easy redemption and you fancy a bit of dichotomy in your characters and your erotica, I suggest giving a shot at "Desire and Devour, Stories of Blood and Sweat" by Jeff Mann. I am not saying that it's the absolute best, but I found it far more satisfying.