These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Love to Hate: Frank has a large fanbase, and is easily one of the most memorable characters in the film.
Love Triangle: Very Subtle. Over the course of the film, Cheyenne gets a bit of a soft spot for Jill. Who in turn develops one for Harmonica. Harmonica's feelings are unsaid and he moves on at the end of the film.
Moral Event Horizon: Frank crosses this in his very first scene, killing a little kid. Yes, Frank is pretty vile.
Tear Jerker: Frank killing off Jill's nice new family. Especially because she doesn't know, and is looking forward to her new life. She's is understandably horrified when she arrives.
The death of Cheyenne.
"Hey, Harmonica. When they do you in, pray it's somebody who knows where to shoot."
The death of Mr. Morton. The sight of it is tragic enough, even more so if you knew what he wanted to do before his death.