Everything is there.
Worn by a variety of styles of writing, changing while changing narrators, perspectives; suspense and some mystery. The book does not fall in the not too great, nor the explanatory SF.
The first two are more surreal tome, offering a multiplicity of narrative and much of almost religious mystery. While the last two volumes are presented more like a road movie, a trip centered on a small number of characters where the mysteries of the first books find their way gradually into a rich and complex puzzle.