Love to Hate: Max Cady is considered one of cinema's classic villains in both versions of the film. Mitchum's portrayal ranks at #28 on the American Film Institute's Top 100 List of Heroes and Villains, and De Niro's version is considered similarly iconic.
Nightmare Fuel: Everything about Max Cady. A cunning, intelligent sociopath who relentlessly stalks and terrorizes the Bowden family with the eventual intent of raping Bowden's wife and daughter before killing them and Bowden himself.
Catharsis Factor: Bowden deciding to not kill Cady while holding him at gun point and instead send him back to prison for life. Both he and the audience know full well that to Cady, it'll be a Fate Worse than Death.
Complete Monster: Max Cady is a smug, slimy sociopath who went to jail for rape and returns later to destroy Sam Bowden, a man who testified against him. He kills the family dog, relentlessly stalks the family and destroys those around them, planning to rape Bowden's wife and daughter before he kills them. He also rapes and beats an innocent woman for no reason just as a means of asserting his power over her and Bowden's helplessness to do anything. He's out for nothing but revenge and doesn't care that he deserved to go to jail for what he did.
Narm: As Buddy Love noticed, Robert Mitchum visibly sucks his gut in after removing his shirt.
Nightmare Fuel: Cady's telling of what he did to his ex-wife (abducting her, raping her for three days straight, and leaving her by the side of the road).
Nancy trapped in a room with Cady with no way to escape. Cady's sadistic expression doesn't help.
A mild example: when discussing how Cady could possibly think he'd get away with raping Bowden's daughter, Bowden concludes that Cady knows that, while her testimony would put him away for life, the devastating experience of having to testify and answer questions about it would be so traumatic that the Bowdens would let Cady go free before subjecting their daughter to the questioning. Nowadays, most people with knowledge of sexual assault cases (which Bowden has) actually encourage victims to testify for their own benefit as much as to help convict the assailant; modern psychiatric help stresses the cathartic effect of testifying against the rapist, and so, however upsetting it may be at the time, the Bowdens stopping their daughter from speaking out against her attacker would be unlikely to help her long-term recovery. (There's also the fact that today, many countries have laws allowing a child to testify by video camera rather than having to be in the same room with their attacker, but that's more a case of Technology Marches On rather than this trope).
Since 1962, awareness of stalking has increased and the law now offers much stronger protection for its victims. With the known history the two characters share, it would've been relatively easy to prove Cady was harassing and following Sam with malicious intent, which would've netted him a trip back to prison for his trouble.
The police initially try to arrest Cady for vagrancy (meaning, in this case, having neither a source of income nor enough cash reserves to live on) and later for "lewd vagrancy" (having a sexual hookup with an unmarried woman). Modern viewers will likely be either confused or aghast that these were ever considered crimes.
Vindicated by History: The film was such a flop on release that it ended Gregory Peck's production company. Now it's considered a classic thriller.
Also contested with AFI's 50 Greatest Villains list as to whether the Robert Mitchum version should've instead been switched out in favor of the Robert De Niro version.
Catharsis Factor: With returning to prison clearly being far too good for this version of Cady—and it also being part of the problem too due to him insisting he never belonged there in the first place—seeing him dragged back into the river and then under it is a satisfying scene, if not it's at the least relieving just because Cady dies after everything he's done.
Complete Monster: Max Cady, fourteen years before the film began, brutally raped and savaged a sixteen-year-old girl so horribly that his lawyer Sam Bowden sabotaged his defense. Seeking revenge, Cady poisons the Bowden family dog; stalks Bowden repeatedly to drive him insane; rapes a friend of Bowden's; and later murders his housekeeper and a private investigator. Cady attempts to seduce Bowden's teenage daughter, his plot being to torture Bowden while raping his wife and daughter, all while Bowden is Forced to Watch in Cady's attempt to "teach him loss" in revenge for a prison sentence he richly deserved.
Genius Bonus: How many viewers were able to understand all of Cady's literary references, especially the "Ninth Circle of Hell" from The Divine Comedy?
When Cady is beating Bowden to force him to confess to having buried exculpatory evidence, he starts conversing with an imaginary judge at the same time, while whipping his head back and forth with a rather silly 'fwip' sound effect.
Cady's death. Before he starts "screaming in tongues" about the promised land, it really just sounds like he's saying several random syllables quickly, most of which are "bloh de blah".
Nausea Fuel: Cady biting off a chunk of Lori's face.
Cady in general is a walking example of this. An utterly depraved, sadistic and terrifyingly intelligent and determined rapist and murderer who will stop at nothing to hurt Bowden and everyone he loves. He's easily one of the vilest bad guys in film history.
Cady's face after having his face burned to a crisp is enough to give you nightmares for a week. If that wasn't enough, how about the weird, gibberish noise he makes while he's drowning to his death, not to mention the Death Glare he gives right after?
Squick: Cady putting his finger in Danielle's mouth and later kiss her on the lips.
Bowden gets the chief of police to try to drive Cady out of town before Cady has done anything illegal. Cady hires a lawyer who is portrayed as fussy and over-liberal, but who makes the entirely legitimate point that Cady is being harassed for no reason. Of course, Cady does not stay innocent for long.
When he also threatens to get Bowden disbarred, clearly the audience is supposed to see him as petty, but given that Bowden failed to act in his legal and ethical duties as a defense attorney to Cady 14 years earlier by burying evidence that could've lessened his sentence, this isn't an overreaction. Of course, given that the evidence that would lessen his sentence is based on inherently wrong logic, viewers are likely to see Bowden as a man whose conscience gave him the strength to go against a twisted law that allows rapists to get away with their crimes.
Values Dissonance: Bowden buried evidence that would have lessened Cady's sentence. Said evidence is a rape victim's sexual history, which is now inadmissible under North Carolina law.
Values Resonance: Bowden was so disgusted by Cady's crimes that he buried a report about the victim that would've gotten him a lesser sentence and later tells Cady that just because his victim was promiscuous didn't give him the right to rape her, a belief shared by many people in discussions about rape in the 2010's which make clear that nothing a victim says or does makes an attack anything other than a horrific assault and violation. Sam's actions now look even more sympathetic and righteous than at the time.
, and De Niro's version is considered similarly iconic.