This series has a super interesting premise, and as a fan of Bryan Davis' other works, I was really excited to dive into this one. However, there were some things overall that put it as one of his lesser books in my mind.
First, the writing style of this series is very different from his other series (like Dragons in Our Midst and the others). There's a common principle called "show, don't tell" which many authors try to use in order to immerse readers in the story. However, this book in particular (and this trilogy in general) were pretty full of telling and overall not very immersive narration, and it made it very difficult to get into the story. Trying to explain the complicated worldbuilding with the three earths and the misty world and whatever "Sarah" was came off as confusing and very difficult to keep track of what was what and who was where.
Second, this is a bit nitpicky, but speaking of "Sarah", as someone who shares the same name, I thought that piece of worldbuilding was... awkward, to say the least. I understand the biblical reference, but the whole concept was really strange and overall I skimmed most of those parts because they were flat out weird (if you've read this book and/or Interfinity, you'll know what I'm talking about). I must not be the only reader named Sarah who thought that was just plain uncomfortable.
Third, the worldbuilding is certainly cool in concept, but so much of it didn't make sense. While reading this book, I basically gave up on keeping track of which duplicates were evil, who was on which earth, and what the dreamscape was supposed to be/mean. I just wish for more clarity and easier to understand plot points (but hey, at least there were no giant bees in this one).
Fourth, thematically, it was only decently executed. The whole thing with Kelly's backstory and the things she struggles with... I can see the intent behind it. However, we only got a skimmed-over version of the things she did in the past, and it wasn't enough closure to bring her redemption full-circle. I understand and respect the caution with revealing what she did and didn't do, but the level of vagueness was just too high to make the theme work (remember, show don't tell). Plus Kelly was basically the only one who had some sort of arc, making all the other characters rather two-dimensional.
Fifth, Nathan's plot armor is the strongest I've ever seen (he is a fantastic character but my word that guy is invincible). So many other characters get harmed in several ways, and the worst Nathan gets is an hurt hand that is more an injury to his pride than anything else.
With those critiques said, I decently enjoyed the series and this book. When I understood what was going on, it was very fascinating and a fun read. Vastly different from most of Bryan Davis' other books, but I thought the ending was well done and the climax actually felt like a climax (as opposed to most novels out there) which was good.
All in all, if you're looking for something new and exciting, I'd definitely recommend this book and this series. If you can wrap your head around the definitive "otherworldly" premise, then this series is for you :)