I think a trailer has to be short, it has to create a certain frustration. The audience has to think "I want to see more!".
The music was interesting, the editing too... The only thing is that sby who see this trailer and then the movie will be just a little surprized, since the atmosphere has nothing to do. So I think it's a good work, but a bad trailer.
You are right about the false adverstisment of the trailer. When watching it, it feels like it's a western with a lot of action. But that's nothing new with Leone's films, if you look back at the Dollars films trailers, they were kind of advertised as the same thing. The people who really love the western genre, I don't think would be dissapoited in the film after seeing that. Maybe your average movie goer would though.