Let's start by addressing the elephant in the room: yes, this film is blatantly 'Yojimbo re-made as a western'. So blatantly, in fact, that the makers of the Japanese film were able to successfully sue, delaying the release of this movie in the US for three years. And even when it finally did hit American shores, it got pretty negative reviews.
None of which stopped it from becoming one of the most successful Italian films released to that date. Probably because, whatever the critics might say, it's a darn fine film.
Whether it's Sergio Leone's visual flair as a director, Clint Eastwood's charisma (he might not do a lot of actual acting in the film, but he can be darn compelling at what he does do), or the iconic soundtrack from Ennio Morricone, there's plenty to like about this film, and it is easy to see why it launched the 'spaghetti western' as an international box office force.
Eastwood plays 'Joe' (likely an assumed name, and the character would later be dubbed The Man With No Name), a drifter who wanders into a miserable little town divided by two rival crime bosses. Joe (which I am using because it's shorter than the alternative) quickly makes a name for himself by gunning down four men, and turns that notoriety to his own ends by playing off the two sides against each other and escalating the tensions in the town. His motives for doing so are pretty murky: this is not the clean-cut hero of Eastwood's Rawhide days.
The film boasts lots of well-staged sequences, both of action and of black comedy. It's by no means a terribly realistic film (though not anywhere near as gonzo as Sabata) but it is consistent to its own tone and conceits throughout, which makes it easy to accept the events on screen.
Quality film-making, and well worth a look.