There's a lot of hype about how expensive this movie was, but I don't see where all the money went (even given the on-location shooting). It is, however, quite a decent movie, especially for the big screen. Kevin Costner plays a mutant drifter called the Mariner, who is saddled with the job of protecting a little girl, Enola, and her pseudomother, Helen. Dennis Hopper plays a convincing bad guy Deacon, the head of the outlaw tribe called Smokers, who is after the little girl since she has a special map tattooed on her back. The map shows the way to the object of many dreams in Waterworld. This object is Dryland, which the denizens of Waterworld have not seen ever since the polar ice caps melted and covered most of the planet's dry surface. Costner's Mariner has adapted to the watery conditions, and has grown gills and webbed feet. This doesn't go well with the "normal" people, and it is shown to us that even a water world will not diminish the xenophobic tendencies seen in humans.
One of the more interesting and better performances is by Tina Majorino playing Enola. This is one case where an obnoxious brat-child performance doesn't annoy, but instead serves to amuse. Costner doesn't speak much, while Hopper is a source of great comic relief. That's probably for the best. The action scenes are amazing, and probably the one main thing that makes it worth watching on the big screen.