For those who have read Piers Anthony's Apprentice Adept series, the idea is a familiar one: The protagonist falls asleep in one world and by this method he awakens in another. However, this book covers a much more serious topic: the destruction of the world by means of germ warfare and the consequences for future generations. (Yes, there is a little bit of a reminder of the Planet of the Apes, too. Get over it.) Dekker is a very good writer, and the characters are also well developed, their actions can be logical. In general, he paints a pretty realistic world.

However, it's also pretty heavy-handed (forget a golden halo; a 2x4 comes to mind). The garden motif is nothing new. It's been used in many books, many BETTER books. What makes this one not as good? It's too heavy. It too much wants to paint the good v evil thing in really obvious strokes. If he's not a religious writer, he's certainly doing a good job of trying to be. Not that this bad. CS Lewis wrote much fiction about this, but he wasn't as HEAVY as this book is. YIKES. The points that occur on current Earth are very well done. The points in the other place are just Oh-my-God-let-this-over-the-top-religious-simile/imagery/this-is-a-book-about-God-stuff end. At some points, you were waiting for him to write in some footnote, "Pssst. This is a reference to Jesus/God/the Garden of Eden...") Want to read some books about religious/garden motifs? Here are a few:

Milton, Paradise Lost
CS Lewis, Space Trilogy
Tolkien, Lord of the Rings trilogy
Assorted Authors, The BIBLE

PS: I'm not reading more from this series.