I thought it was pretty good, a few nifty twists and turns, and Costner hasn’t irritated me yet.
Couple questions
What was the deal with the bad accident in the beginning?? Who/what? Was it connected with “you owe me a horse?”
Who was she fucking, and what was the meaning of it??
I actually just started watching it yesterday since it showed up on Sling’s Paramount channel. I put it off because I can’t stand Kevin Costner because he always plays the same part of a better than everyone else hero. In this one he plays a totally evil person, so I’m gaining some respect for Costner as he gets older and actually does some acting. 
I believe that the accident was caused by a construction company that was going to do work on the Indian reservation to dam up a river that would have affected Costner’s land holdings and that Costner was almost killed by the wide load truck carrying some sort of bulldozer. Costner had to shot his horse. It sets up the battle between the rancher (Costner) and the Indian tribe.