Here's a bit of a caveat.
Acheron is not a bad book, but I still wish I hadn't read it. It just destroys too much of Ash's mystery and brings him down to our level in a way.
So I looked forward to getting back to normal, after that exercise of torture. :) (Pun intended)
Please note: The blurb of One Silent Night is COMPLETELY wrong.
If you expect a christmassy book -- don't.
Aside from the final events, it has nothing to do with Christmas.
That's just marketing, because of when the book was released, is my guess.
About the only thing right in it is that there is an angry ex. The Dark-Hunters barely get a mention, let alone join in proceedings.
Whoever let the blurb through saying "Son" instead of "Daughter" needs to be made to re-read the book. Shoddy, really shoddy, but not Sherrilyn's fault. That one is down to copy editors, editors or marketing people.
OSN is more about setting up future novels and establishing the new order of power, than it is about Stryker and Zephyra.
Sorry Sherri, but I felt seriously let down, because I know you can do much much better.
The characters lacked depth. Too much "I hate you" followed by "I'm sorry" to really have a conflict.
Stryker suddenly has a heart. I suspected he did, but he deserved so much better than this book. He deserved better than Zephyra, too. It didn't make me perceive him as the strong, unshakable heroes I'm used to from Sherri. Instead my sense of strength that I got from him in previous books, evil and malicious as it may have been, transformed into a sense of "What kind of spineless weak git is this?". We keep being reminded what he's capable of -- but it felt more like "Remember, he's really evil".
I didn't like Zephyra. Or rather, I built up no empathy for her. I can't even recall what she looked like, and I put the book down an hour ago. Her power is too convenient and often feels like a cop out.
There is way too much setup of pantheons and their interactions to get a decent sense of the people whose story this is supposed to be. And they deserved better than being thrown into this hodgepodge of storylines.
There's too much Ash, Savitar, Nick, Jared, Artemis and whatnot involved, along with a whole slew of new and old gods.
Too many events smack of deus ex machina. (WAY too many.)
Too much tell instead of show.
Too much explanation where I could have done without, not enough where I needed to know.
And throughout -- there is a lack of the tension that made the previous books keepers.
The previous books (apart from Acheron, where this trend started) were about people, not about the world around them. This time it's more about the world and the powers in them and who does what -- with a bit of gratuitous sex thrown in -- than about the people.
All in all, I'll only recommend it to keep on track with the series, but other than that... I kept getting bored.
I was more interested in reading about Davyn than Stryker, more intrigued by Medea than Zephyra -- and that's bad, when it's not their story.
I know I'm a harsh, brutal, critic, but I also know Sherri can do better than this.
I'll still get the next one, in the hope we return to previous keeper books, but chances are slowly running out. Stop worldbuilding and start writing about people again.