I've worked in libraries for years including a few in Texas, so it is a wonder that I've never read a western. Part of the problem then with reading your first book in a genre is that you lack the language to properly describe it or make comparisons. Now I wonder if I shall ever read another for the fear that the next one won't hold up to The Sisters Brothers  by Patrick deWitt.
It is the gold rush years and the infamous Charlie and Eli Sisters are riding from Oregon City to San Francisco on orders from the Commodore to kill Hermann Kermit Warm. There is trouble with horses, whores, a red bear pelt, excessive brandy drinking, a man named Mayfield, a witch and a mysterious magical formula. Large sums of money come and go. The characters are unique, but without a lot of overall development. Is this usual for a western? Is the level of violence similar to other westerns? Is this a parody of the genre, a homage or both?
The introspection provided by the first person narration provided by Eli is darkly humorous, gritty and shockingly thought-provoking. The style of language was unique but never felt forced and I was drawn in immediately. Short chapters provide a fast pace, even when there isn't a lot of action.
While reading about this book, I came across term that was new to me: picaresque. A picaresque novel is one that is written in first person narrative in plain language and features a main character of a lower class (from rogue in Spanish). Reading about this novel description, I see that one of my favorite books, The White Tiger  by Indian author, Aravind Adiga is also identified as a picaresque novel. And though the settings on paper are entirely different, the themes of both The Sisters Brothers and The White Tiger are somewhat similar. And while both books on paper don't fit my comfort-zone reading, they both stand out as memorable fiction. Both books also passed some critical muster when The White Tiger won the prestigious Man Booker award in 2008 and The Sisters Brothers was on the 2011 short list. I don't know if regular western readers will enjoy this, but fans of literary fiction might give either unusual novel a try.