I realize I'm starting to lose my credibility when I say I never say this, but, again, I really liked the movie better.
I first saw the movie when I was a senior in high school, and it instantly became one of my favorites. It just made so much sense to me--the idea that heaven and hell are not ruled by a human-like god, but rather are what we make them in living our lives. It was broad-brush about the details, to be sure, but on the other hand, it really didn't need to fill them in.
The book tries to explain too much. It gets into the mechanics of reincarnation, spiritual doctors and gurus, psychics, and the "science" of it all--it ends up just being hokey.
It feels heretical to say it, but watch the movie, skip the book.