Generally- an inoffensive fun book if you want some Scooby Type Shenanigans with adults. My heebies were jeebied and I liked watching everyone come back together and grow and develop.
More Specifically- 

The  bad guy's "why not" reasoning about summoning the apocalypse... Wasn't super compelling? Like just. He had no reason to try this hard for this long other than "why not"??

The atmosphere created and written was really well done and yes, my heebies were jeebied.
Also the dog lives, which is all I could ever really want.