It's very sad to see Laurie Strode, the same innocent teenage girl from 1978 without a care in the world, becoming a paranoid wreck who's lived every day of her life in fear that Michael could one day return. They don't hide how broken she is by that experience and how it's affected her, even after 40 years.
Even worse, Laurie's trauma damaged her ability to properly parent, estranging her from her daughter and the rest of her family even as she tries to be a good grandmother to Allyson. It's genuinely saddening that Karen lies to her daughter's face about contacting Laurie for their meeting her boyfriend Cameron, and that Allyson had to make sure Laurie was invited herself.
Karen’s childhood in general. After surviving her ordeal with Michael, Laurie was so paranoid in wanting her daughter to be able to defend herself the day Michael got out that she essentially put Karen through Training from Hell with social services eventually deeming Laurie unfit to care for her daughter and took her away at the age of 12.
The scene where Laurie breaks into Karen and Ray's house, and snarlingly condemns her daughter for her stupidity in not having better defences prepared. It's truly heartbreaking to see Laurie being unable to relate to her daughter on a human level, as a mother, instead laying into her for her perceived faults in not being prepared for a murderer incarcerated since before she was born. Imagine hearing that from your own mother, of all people. Poor Karen looks and sounds likes she's about to start crying as she and Ray shoo Laurie out the door.
The scene where Laurie arrives at Allyson's family get-together is crushing, as the emotions of seeing Michael depart on the bus to the new prison get the better of her and she breaks down in front of everyone. What's particularly sad is the way no one but Allyson tries to comfort her after she flees rather than ruin their family meal. Karen just criticises her for bringing her up so badly while Ray's clearly at the end of his tether at it all.
There's something about Karen's little speech to Laurie that the world is full of happiness and love when she's kicking her out of her house that's soul-destroying considering that she ends this Halloween night with her husband dead, her daughter traumatised by the night's events, and her life in ruins. Reconnecting with her mother is about the only plus she can take from it all.
In a similar vein, Allyson asks Laurie early on in the film as to why Laurie just doesn’t get over what happened in 1978 and outright commands her grandmother to “get over it.” By the end of the film, Allyson is going to realize that’s easier said than done.
In general, the film defies the Developing Doomed Characters trope most horror films fall in by adding tiny bits of characterization and humanization to a good number of Mauve Shirts, making us feel sorry for them and to magnify Michael's senseless killing and cementing him as a monster:
The fate of the son who finds the bus crash accident. His father leaves him alone with a bunch of escaped and potentially dangerous patients wandering around in order to survey the scene, and the son is eventually forced to leave to tearfully search for him, growing visibly more frightened and panicky when he can't find him. After accidentally shooting Sartain, he returns to the car... only to be attacked and killed by Michael. Along with Dana, he acts as a Sacrificial Lamb, but also as a Wham Shot to show how Ax-CrazyMichael has stayed after 40 years, and he has never killed a preteen in the series before (he did try to kill his young niece in Halloween 4, 5, and 6). Doubly so when recalling the original, where Michael let a fleeing Marion Chambers go and ignored Loomis in order to steal the car and escape; it would have been fairly easy for Michael to have simply taken the car and left while both father and son were out of the vehicle, but he did it just because he wanted to, showing how much worse he's gotten over the decades.
The icing on the cake in that scene. When Michael first grabs the boy, you can briefly hear him scream "MOMMY!" before Michael chokes him and ultimately snaps his neck.
The death of Dana is made even worse by the fact that Aaron arrives in time to try and help her, but his attempt at a Heroic Sacrifice goes tragically wrong, with him ending up used as a battering ram and living long enough to watch as Michael breaks her neck.
The death of Vicky is pretty upsetting, as it's established she's quite a good person and when attacked by Michael, her last act is to scream for Julian to run and save himself. Then her boyfriend, who could be set up to be a coward and flee, goes to try to save her, only to be overpowered by Michael.
It's especially sad because, for a slasher movie couple, they're actually quite a nice pair and get some decent characterization before being killed.
And if Michael couldn't be more of a dick, he takes Dave's heart-eyed jack-o-lantern that he made for Vicky, shoves it in Julian's aquarium, and places Vicky's corpse next to it.
Michael murdering Oscar is also quite sad as it's made clear that he's largely a nice guy who is kind of bullied by his seemingly only close friend, Cameron. It's made worse by Allyson's rejection of his advances, as he had a secret crush on her and because he's stalked and killed by Michael immediately after.
Allyson's reaction when she finds him. She clearly is concerned for him, and when she finds his corpse, her reaction is to be in utter shock and brief mourning. Even if she made it clear she did not see him as a boyfriend, she clearly was dismayed to see him murdered.
Worse still, the third movie reveals that Oscar's mom hanged herself shortly after.
Hawkins getting murdered (at least until the following movie revealed he barely survived the attack) by Dr. Sartain. What's worse was that, besides Loomis, he was Laurie's most reliable ally and was closest to stopping and killing Michael.
The baby is going to grow up without their mother, and without any memories of her beyond what can be found on film or digital media or heard secondhand through other people.
