This is probably one of the best westerns out there and it is so underrated. I know several people who have claimed to love westerns and had never even seen it.
I would say that along with
The Man Who Shot Liberty Valance also
The Good, The Bad, and The Ugly,
Silverado,
Unforgiven, and
Mavrick are all must watch for anyone wanting to tell a western story. You get a good cross section of styles and types of stories that are still western.
Tombstone as well, of course.
Plan to download this tonight and give it a go, as a Texan myself I hope any dialog issues not fitting the setting aren't too bad.