(Review is only for the first two seasons)
I came into this show not expecting to like it but the storyline, acting, and cinematography is superb. Basically it's Mafia Wars in Montana with intermittent giant doses of testosterone (cowboys with guns on horses while fishing)! Costner is a master actor as lead of the Duttons. The show is at its finest when it shows the chessboard moves the Duttons and their enemies engage in.
The show gets gummed early in the second season but starts rolling again midway through. Kelsey Asbille is the weakest link as Monica and plays a poor hand badly, the storyline jettisons awkwardly out and the acting just misses the mark.
I think Cole Hauser as Rip may be the strongest acting (sans Costner himself) and looked forward to all the scenes Rip was in. Thomas Rainwater is great too. The storyline hums and the scenery is beautiful.
Just as Cormac McCarthy's "All The Pretty Horses" was a little more raw and brutal than the title suggests, this show strikes in a similar vein. Highly recommend and wish I didn't wait so long to watch it.