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.
"Funny Aneurysm" Moment: Among the souls encountered during the brief flight of the glider is a pilot of the Space Shuttle - who died, in Carpentier's future (it was written in 1976), when it suffered a failure of the heat shield, and well..."halfway down and going like a meteor when we got a burnthrough under the nose" took on terrifying truth in 2003.
"Carpentier. What will you tell God when you see Him? Will you tell him that He could learn morality from Vlad the Impaler?"
Values Dissonance: The constant conflict between the strict Christian morals demonstrated in Hell and Carpent(i)er's modern, secular values (probably also those of the authors) lead him to conclude that God Is Evil. However, the fact that most people nowadays are uncomfortable with the concept of infinite damnation for finite sins leads to a Family-Unfriendly Aesop: anyone in Hell can escape if they can get over themselves enough to seek redemption. Even if their punishment involves complete immobility or vigilant guards. Then again, there seem to be souls whose duty is to guide others, including Benny - and ultimately Carpenter himself.
Dante's Inferno was also based on older concepts. The sequel is post Vatican 2, and thus deals with it very differently in dealing with the values dissonance.
The guards almost never stop anyone from going deeper into hell, as very few believe anything exists down there but worse punishments. And the sequel has Carpenter dealing with the people that are trapped and immobile, trying to prove to himself that his idea that anyone can leave is correct.
The middle ring of the seventh circle is the Wood of Suicides in Dante's Inferno, with a sideline in punishing the "violently wasteful" (profligate). Now, the wood is gone and the profligate are far more numerous. (Examples in Strawman Political).
Adaptation Displacement: Few fans of Suspiria are aware that this is supposed to be a sequel (to be fair, the two films have little in common plotwise, other than the overarching mythology, which Suspiria makes almost no reference to). The third film remedies this by directly referencing the plots of the previous two. However, fewer still are aware of the Thomas De Quincey poem, "Levana and Our Ladies of Sorrow", on which the mythology is based.
Alternate Character Interpretation: Mater Lachrymarum is heavily implied to be hypnotic and meddling in Mark's life while in Rome. How much of what follows is someone else's idea?
Anti-Climax Boss: Mater Tenebrarum, whose demise occurs due to an accident earlier in the film.
Never Found the Body, though. Tenebrarum's death is far from clear, as she simply vanishes amid rising flames. She'd previously disappeared and reappeared in a mirror just a scene prior, and her transformation into Death presumably makes her more difficult to kill than Suspiriorum in the previous film.
...So, nobody thought to check out Madelyne's DNA to see if it matched Jean's?
Why didn't Sinister just use Cyclops and Jean's DNA to create the baby instead of going to such convoluted extremes? Made even worse because that's exactly what he does in the Alternate Reality crossover, The Age of Apocalypse.
Chalk it up to being written in the 1980s before "CSI" made everyone an inexpert forensic scientist. DNA testing was advanced significantly in the 1990s, which coincides with its appearance in many crime shows.
Moral Event Horizon: An attempt to kill a dozen innocent babies including your own infant son just has to count as this.
Nightmare Fuel: Many instances, but particularly when Madelyne tries to kill her own baby.
They Wasted a Perfectly Good Character: The demon chessmaster N'Astirh is introduced, and killed, in this story arc. Given that he's just another magic-user, fans who think Belasco, the sorcerer who turned Illyana into Magik in the first place, should have returned for this instead consider his introduction to be this.
The Game Mod
Best Level Ever: "Nemesis", the penultimate mission in the original story, has been praised as one of the finest Battle of Endor missions the community has ever produced.
Demonic Spiders: The Vindhacyl bomber. Uniquely, it's only so because of how hard it makes any Escort Mission. Inferno-issue super-painful bombs, a not-shabby beam cannon in a forward turret, and ridiculous amounts of shield HP make it nightmarish to fight in an interceptor because you just can't hurt the thing.
Only the Author Can Save Them Now: What exactly humanity was supposed to do against something like the Gargant was never really answered. Whether the Gargant still exists is also up in the air.
That One Level: "Nemesis" is also considered this by many, because of its sheer length (playthroughs can run as high as 25 or 30 minutes) and existing long prior to a practical "checkpoint" system like in Blue Planet to allow restarting from mid-mission.