It's been a long time since I read the first three books in this series, so I have relatively vague memories of the various kids. Still, I recalled enough to know that this is the first time the twins Sandy and Denny get to enjoy the spotlight. It's a pleasant read that nicely straddles both the line between child and adult, and between religious faith and scepticism. It is by nature a religious story, but not so much that it hits you over the head. The twins themselves seem unconvinced by the end of the book.
All in all, a nice read that doesn't so much continue the Murry story's family, as send two of its characters on a tangential adventure.