Kurt Vonnegut: Sirens of Titan

Sirens of Titan was Vonnegut's second novel, and many of the themes present in it show through in subsequent works, though later works felt more refined.  For instance, the humanist religion in Sirens of Titan, The Church of God the Utterly Indifferent, felt less relatable than Bokononism and more likely to provoke a negative reaction out of traditional believers, though the two religions are very similar at a deeper level.  

"I was a victim of a series of accidents, as are we all."  Classic Vonnegut.  Only, "So it goes" is simpler.

I think that Sirens of Titan was more explicit on the question of free will than many of his other books, though.  One of the chief objections that believers in free will have against determinism is the idea that if everything were determined, there would be no point in doing anything.  Vonnegut answers this objection from both the ends of joy and pain.  One of the protagonists commits an action, based on someone else's will and not their own will, that they regret tremendously.  And some characters, after learning that they have been controlled, argue that "A purpose of human life, no matter who is controlling it, is to love whoever is around to be loved" and that "The worst thing that could possibly happen to anybody would be to not be used for anything by anybody."  Vonnegut also advances the prime objection to the notion of free will -- the idea that "The most significant accident that happened to you was your being born."  If we didn't have a say over our birth and if that one accident is the most significant influence over every choice we have supposedly made after being born, then those choices seem to be much more historically contingent than freely made.

In all, Sirens of Titan is a good read for a Vonnegut fan, but it might not be quite as good as Cat's Cradle if you're just getting started with his works.