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.
Complete Monster: Subverted in William Munny himself, he is really a Retired Monster. While it doesn't seem like he necessary enjoyed killing, in his youth as a bandit, Munny was a cold blooded mass murderer - killer of women, children and even animals. The events of the movie bring him out of retirement.
Hollywood Homely: Delilah's scars aren't exactly pretty, but they don't exactly make her horrible either. And considering she is a small town prostitute, it's not likely her customers would care much. In fact, she's still the prettiest of the girls. It's Lampshaded, though.
This trope is invoked as part of the plot is that the other prostitutes exaggerate just how horribly Delilah was mutilated (they go so far as to claim her breasts were cut off), mostly because they can't actually afford what they are offering and hope the bounty hunters will be driven by enough righteous fury that they will take out their targets before they ask for their money.
And also turned into a Crowning Moment of Heartwarming when Munny tells her that he declined her offer for a free advance on the bounty not because of her scars (of which he has his own, he tells her), but out of being faithful to his wife.
Holy Shit Quotient: After leaving the saloon and on his horse, under the rain, Munny delivers one of the best Badass Boasts of all time: "You better bury Ned right!... Better not cut up, nor otherwise harm no whores... or I'll come back and kill every one of you sons of bitches."
Magnum Opus: A definite contender for Eastwood's as a director.
Little Bill, lecturing to Beauchamp about how hard it is mentally to carry a gun, promptly pulls a gun out of a drawer and offers the writer to use it and help English Bob escape the jail. It's loaded. Demonstrates both Little Bill's hard-learned skill in reading other people - knowing Beauchamp wouldn't shoot - and his sadism by encouraging English Bob to get the gun from Beauchamp. It's when Bob sees Bill's grin turn into a sneer - and ready to pull his own gun to "shoot in self-defense" - that English Bob refuses the gun.
They Really Can Act: The whole male cast (at least) is on the top of their game. Clint Eastwood turns in an impressive performance as William Munny, which earned him a Best Actor Oscar nomination. Gene Hackman's chilling and sinister portrayal of Little Bill Daggett won him the Best Supporting Actor Oscar, as well as a slew of other acting awards, such as the Golden Globe and the BAFTA.
The Woobie: Delilah. When William Munny is trying to tell her she's still beautiful with scars while not betraying his late wife, you just feel so much for both of them.