Good book, but a masterpiece of science fiction it's not.

Mostly, there's not much science there. If you think of SF as speculative fiction, there's also not much speculation there.

Although it starts from a classic SF premise, it quickly turns into a political and spiritual introspection of the protagonist. That is interesting in many ways, and I could discuss the themes for hours on end.

I guess it's one of those misclassified books, like Lem (who insisted he wrote philosophy, whilst writing much more hard SF than this work), or some of Piers Anthony's writings.

Great read, but don't expect SF.