I started reading the Riverworld series last year and finished the fourth book (the ending) tonight. It's a cool scifi concept - everyone who has ever died gets resurrected on a world with one big river running through it, in a valley bounded by unscalable mountains. It essentially one big one-dimensional world, and it started off with such potential. Unfortunately, the ending is disappointing. Just read the amazon.com reviews.
I recommend reading the first book, and just leaving it at that (it's has a somewhat satisfying ending). I don't have much else to say about this series, but you can tell that I'm a little incensed by the anti-climacticness because I'm bothering to blog about it ! I took quite a bit of pleasure just reading the amazon reviews of the fourth book, so I can nod my head "right on brother!" As I said, the first book was well-written and is worth reading, so don't let my review turn you off completely. Just ignore the other three books. I wished I had read reviews before picking up the series, but I figured it must be pretty good since the Sci-Fi channel was making a series of it. A lesson I learned... :)