'Dances with Wolves' because it fundamentally changed the narrative of a Western. Native people were shown in a completely different role, and the atrocities of the time were not ignored. The slaughter of the American bison and the indigenous people and cultures were shown quite graphically. No movie had ever done that, and there aren't many that have since.
Sam Peckinpaw movies and anything with Slim Pickens makes the cut. With that, I mention: Pat Garrett and Billy the KidRancho Deluxe has a cult following as does El Topo.
The Wild Bunch for sure.Here's a couple of wild cards from around 1970..........Ned Kelly with Mick Jagger playing the lead role and A Man Called Horse with Richard Harris playing the lead. Both very interesting and entertaining. Other than that Lonesome Dove and Jerimiah Johnson.