There is a reason why some spinoffs won't work. When an author takes a beloved sidekick and tries to give them a separate story, my first question is, do they have main character energy?
Is there a presence so strong, that you could write a standalone about them, that would work even without previous books?
West was a great addition, but I won't lie. First-person narration robbed him immensely of his charm.
Something was missing for me in the story and in the romance. I couldn't really get existed for West and Rez. Instead of banter, we got a lot of deep talks, support, and understanding mixed with guilt. It felt more like he hooked up with his therapist. Yikes.
Where is entertainment in reading about relationships with no tension? At least I didn't feel it. Until the few last chapters book was quite boring really.
Plot... it was only there to propel forward the relationship. I couldn't really care when clearly everything happened only to make them defend each other or to bare their souls to each other. It shouldn't be obvious to the point where the reader dissociates from the story.

The fact that there were no other characters, no world building showing us the aftermath of barrier destruction only solidifies the impression of story being underdeveloped.
Nothing changed in life in Ireland? They encountered no independent fae or any prejudice from locals? Five-star hotel was just standing there in some village after the world practically ended? First asked bartender knew the guy they were looking for and was the only person LIVING that knew he is not dead and in hiding. It led them to the next very convenient clue. Why Rez was even kidnapped? Some random tarot reader gave them keys to the cottage just next to the place of the final battle? Tell me about a half-baked story.

There is also another aspect that bothers me. While West lost much, he still has his family, his home, which now he appreciates more, he got the girl and has a hope of getting his beast back. While at the same time Rez lost EVERYTHING. This elegant, sophisticated woman sacrifices everything for a guy. Her home, her family, he even changed what she wears. That doesn't sit well with me.

I also wasn't feeling the narrator. Some men just can't make female voices. Every female character sounds the same, like some flimsy dolly. When for Rez it was bearable, Amber with this voice just made me cringe