Really, really, good book spoiled by a particularly disappointing movie.

In the book, you get to live to 30 - and that's it; no metaphysics about being reborn somehow.

When the book was written, many of us worried about what appeared to be an oncoming Malthusian disaster (too many people / insufficient resources). The book was a response to that (i.e., have as many people as you want - but you only get 30 years). The movie just plucked out a chase, with a background of 'future stuff', added in some nudity.

TL:DR: if you've read the book, skip the movie; if you've seen the movie and are considering the book - it's pretty good