This is one of the most important political spaghetti westerns, a surprisingly large sub-genre because the opportunity to set the film during the Mexican Revolution gave a lot of scope to directors with a strong left-wing bent, and of course, since these directors really cared about the message they were trying to put across, left-wing spaghetti westerns tend overall to be very good.
Damiano Damiani had a patchy, largely undistinguished career, and this was probably his finest hour, except perhaps "My Name Is Nobody", a very different kind of western which may have been partly directed by Sergio Leone. The two men obviously influenced each other, since Leone's last (and worst) western "A Fistful Of Dynamite" is close to being a remake of this film. Both movies are about a chaotic, largely amoral Mexican bandit supposedly fighting for the revolution but mainly for himself, who forms an unlikely friendship with a wily gringo, and eventually learns what it truly means to be a revolutionary. And of course, along the way, lots of people get shot, things get blown up, and so on.
Damiani lacks Leone's visual flair, but you could say that of almost all directors. And he does add some very distinctive touches. Everyone remembers Klaus Kinski's mad monk delivering a benediction which he punctuates by lobbing grenades, but I was particularly struck by the way that, although films of this type virtually always portray the government troops as faceless cannon-fodder led by a sadistic madman, for once Damiani bothers to show us that the rebels' enemies are human beings too, some of whom have highly admirable qualities, so every death genuinely matters.
Of course, plenty of luckless guys in beige uniforms die all the same, probably about a hundred, so there's certainly no lack of the kind of action you're hoping to see. There is, however, a stronger emphasis on character development than usual, even minor characters who otherwise wouldn't matter. In fact, the entire movie is basically about how our extremely flawed hero El Chuncho's character develops. This is perhaps one of its weaknesses, since it does become a little preachy at times with its rather obvious "will Chuncho be seduced by money or do the right thing?" message.
The casting is also slightly odd. Gian Maria Volonté, the extremely memorable villain from a couple of Clint Eastwood movies with "dollars" in the title, is well over the top at times. This was apparently his main failing as an actor, which Sergio Leone kept more or less in check by making him rehearse his scenes so many times that he was too tired to chew the scenery by the time they pointed the camera at him. Unfortunately he doesn't seem to have told Damiani about that little trick. And Lou Castel is so unappealing on every level that it's hard to see why certain other characters are instantly attracted to him even though he's clearly a calculating self-centered reptile from the get-go, unless the part was originally written for an actor with more charisma - Terence Hill, perhaps?
All in all, this is a slightly flawed but very good Italian western that takes itself more seriously than most, but doesn't compromise on the violent action its target audience came to see.