If you're a fan of Costner's epic films you can skip this one because it's not one.
The movie has no flow of a consistent storyline. It's like he took a bunch of episodes from TV miniseries and strung them together with the only common factor is that some, not all, of the characters stopped at the wanna be frontier town of Horizon. If he had stuck with the revenge, or love story, or conflict of native and white cultures then it might have been worth 3 hours of my life just for part 1. The last 5 minutes is a montage of scenes from part 2 that you have no warning of. Makes me feel I've already seen the second part