I actually bought this film because it was one special offer. It was one of those buy three for £12 or something and I needed to make up numbers so I went for the longest film I could find.
I was therefore pleasantly surprised when I watched it and it turned out to be pretty good. The plot is a bit farfetched with the notion of a postapocalyptic world in which Costner can essentially reprise and slightly modify his roles in Dances with Wolves and Waterworld.
I was a little dubious about this premise and I usually despise films which glorify the US beyond all recognition, such as U-571, and The Patriot, so I do kinda agree with one of the other reviewers because it does spoil the general feel of the movie. Having said that if you can ignore the blatant patriotism it is a good action/adventure movie.
The main reason I didn't give it 5 stars is because of its focus on America and all the generic notions of freedom the theme inevitably projects, and becuase it is slightly too long, most people do seem to get bored, but I liked this film and Costner does puts in a good performance as both actor and director.