All I'm going to say without seeing the movie is that if you just see the movie and don't read the book or don't plan on reading the book, SHAME ON YOU!
It's too late for me now. I've been told this so many times it's ruined me and I know I'll find a way to hate it. It's unavoidable.
It won't be its fault, so I'm not going to read it. No sense in tearing something down that doesn't deserve it.
I never saw 'American Beauty' either, for exactly the same reason.