On another level the story is a cosmic battle between the forces of darkness and those of light. This level brings a sense of surrealism to the story. For example: Vincent is dead and Isabelle, who brought him back to life, is caring his baby. This baby is a sort of savior of mankind and as such has supernatural powers as does Ettrich the undead. Ettrich and Isabelle must not only unravel the problems of their own lives, they must untangle the mystery of Ettrich's death. Within this struggle, the meaning of life is explained. I won't go into all the details in case you want to read the book yourself but it gets rather metaphysical and hard to follow at times.

Both of these levels work in some way. The story is intersting and there are enough twists and turns to keep the plot moving. The writing is fresh and lively and keeps the reader interested. But the two never really intertwine in such a way as to elevate the book from interesting to insightful. The conversations and thoughts on relationships and life are strong and enjoyable but the overall metaphysical punch is laking. If you are going to try and create an alternate meaning behind the universe you need to have either a unique insight or a really cool concept. White Apples doesn't quite reach either. It comes off as kind of a neat new age love story without the philosophical meat. I think Publishers Weekly got it about right:

The story is a classic Carroll romp in which personified states of mind achieve independent life, characters interact with quirky incarnations of aspects of themselves, and bizarre metaphors ("When you're dead they teach you how to make a water sandwich") are illuminatingly literalized. But Vincent's puzzlement over his quest and the iconic roles others play in it demands talky explanations that interrupt the spontaneous flow of fantasy and suggest the author has overreached in his stabs at inventive symbolism. The novel boasts its share of the fresh perspectives on life and love that Carroll's fans have come to expect, but readers may finish it feeling a bit like Vincent, more instructed than entertained.

Overall, I would say if you enjoy thought provoking fiction in the "magic realism" vein, or you just like interesting stories about life and love, then White Apples would be worth your time. But if you are looking for real philosophical or existential insight you will likely be disappointed.