3.5 rounded up to 4.
There's a whole lot of things to love about this novel. As others have said, it is very much a slow burn of a horror novel, with Sullivan taking his time to set the world, the tone, and make you feel the losses. I think one of the biggest strengths of this novel, and the part I enjoyed the most was a wonderful, beautiful, healthy, loving relationship between Devin and Connor. It just worked for me.
Some of the things that brought the score down a bit were...
The pacing. Again, as others have said, I do believe the novel to be a touch overlong. Sullivan's writing style is excellent, if a touch too detailed at times. It did slow the narrative down a bit.
There were also a couple of times—again, no spoilers—around the disappearance of one of the children, and also around Devin and Connor considering when to leave, that I felt were not treated realistically, as time didn't necessarily be of the essence in either case. I kept finding myself saying to the involved parties, "Oh, would you hurry up?"
Moreso toward the ending. Without spoiling anything, I will say the author intercuts flashbacks in around the ending. I understand fully what the author was doing and why, however some of the flashbacks seemed a touch repetitive, having already gone through parts of those scenes earlier in the novel, and the sheer number of them did get a bit much.
As with any indie release, there were a few grammatical and editing errors and—at least in my experience—like most indie releases, they did tend to multiply toward the latter third. However, they weren't egregious, but it does tend to impact my enjoyment of the writing style.
Finally, and I believe this may have been more noticeable simply because there was just shy of 500 pages to read, but the shift from black type to a dark grey, then back again was irritating. For this, I place the blame squarely on Amazon's printing, as I've seen this too many times for it to be anything else.
So, for me, the biggest factor was the pacing. I think this could have been a mind-blowing, stellar, absolute 5-star read as a 350-page novel.
But, for all of that, it's still an absolutely excellent read that deep dives into the characters and truly does examine grief in its many forms. Definitely worth the read.