I read it because I'd seen the film. I was expecting more divergence than is normally the case. The film has startling imagery; the book has excellent prose description to balance, though they do not always match. Details differ (e.g. the fate of the diary), but not disconcertingly so, and the weight given to various spans of time also differs between film and book. The character of Pi is an unusual one - not very "traditional Indian", but the contrast with his family is important to the story, so I don't quibble there.
I was going to compare it with Paul Coelho's "The Alchemist", but it is far superior to that dismal fable. Better might be to compare it with (say) Primo Levi's account of his life in a concentration camp "If this is a man", both telling of how a man might lose so much of his civilisation in a hostile environment, yet retain aspects of humanity.
One might contend that Levi's work is "true", whereas Martel's is fable (and therefore innately "lesser"). However, Martel echoes Pilate's question: standing before God - What is truth? Which of Pi's stories is the true one? Martel contends that it doesn't matter if both tell a similar tale of the heart. Pi knows that God is not fooled, but may still be more amused by the "story with animals".
I too was amused, and intellectually provoked, by this story, but it doesn't feel like a book to which I'll return.