Have to agree with the previous post that it is rare I say this, but the film adaptation is, to me at least, much better than the book.
(The other films being better than their respective novels, The Godfather, A Clockwork Orange, and Silence of the Lambs, obviously not just sci- fi related)
I will also have to admit, being a big fan of PKD, that this is almost an apples to oranges comparison. These two pieces, the book and the film, are entirely two different stories with the names of the characters being the same.
When I first saw the movie, during the theatrical release, I thought it was good although a bit long and tedious. After having seen it numerous times and through all the different versions, the movie has become a classic in my own mind. Not just of sci-fi, but movie making in general.
The book was still good, but didn't have the same meaning to me as the flick. My favorite PKD novel being "A Scanner Darkly".