With apologies (not really) to fans who disagree, this is truly a classic western. I read a criticism that some scenes run long with agonizingly lengthy close-ups, but I found the cinematography intriguing. Those shots divulge nearly as much into the characters' personalities as a wad of dialogue from older traditional westerns.
Sometimes in a spaghetti western I find myself thinking, aw, why did that innocent person have to die, but innocents did die in the old west, I imagine. I am sure there was a lot of senseless violence then, just as there is now. And Bronson seemed like an odd choice as hero to me, though who can question a director who had the instinct to make perennial good guy Henry Fonda the ultimate villain? He didn't suck in this role, did he? And at least we get some back story with the harmonica playing Bronson character, unlike with old Blondie from Leone's The Good The Bad and the Ugly.
And if you like the soundtrack, check out a YouTube video by The Danish National Symphony Orchestra And watch how they recreated the various parts of the music. It is pretty neat and just eight minutes long.
So yeah, I think Once Upon a Time in the West is a western classic, a Greek tragedy with spurs. So shoot me (at ten paces).