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.
Common Knowledge: Everyone "knows" that Frankenstein is the creature, or at least used to. Nowadays it's fairly common in fiction to hear one character snootily correct another about it being the name of the scientist and not the monster.
I Am Not Shazam: Many people call Frankenstein's Monster "Frankenstein", while he actually has no name. "Frankenstein" is the name of his maker, Victor Frankenstein. But we can probably blame Mary Shelley for that; it would be a lot clearer to all if she'd called her novel "Doctor Frankenstein". This confusion dates back nearly as far as the novel itself, and became established during periods when the actual book was out of print, but its characters and plot were being emulated by stage plays, knockoffs and parodies throughout the pre-copyright 19th century.
Ironically, since one could argue that Frankenstein is the "father" of the creature, you could say that the creature's last name is Frankenstein.
Either Victor Frankenstein is a tragic and naive scientist who - in his enthusiasm - bit more off than he could chew and paid a horrible price and suffered too much for it and has every right to be emo about it OR selfish asshole who tried to keep his PR clean by abandoning the monster and got what was coming to him and he's being whiny about it.
And the monster is either a far bigger woobie than Vic could ever hope to be, abandoned by the only person he could possibly consider a parent, or a wangsty monster with a Freudian Excuse who needs to take responsibility for his actions?
Broken Aesop: The fairly anvillicious message is that humans are not supposed to play God and Victor Frankenstein expressly says it was wrong to create human-like life the artificial way. However the humanoid he created was much smarter (learning language very quickly for instance), stronger, quicker (not in the films, but in the book) and more moral (despite raised without guidance, he had an innate desire to belong and do good for the greater community, the monster becomes vengeful only after consistently being persecuted for no reason -a human treated like that would have been vengeful pretty much immediately) than any human life he could have created the regular way. The tragedy that unfolds easily have been avoided: Victor Frankenstein could have put a bit of effort into making his creature look acceptable to humans, he taken care of his creation (anything more than just cruelly abandoning the newborn confused creature would have helped greatly), if the humans he approached had not been such complete dicks, if the monster had realized how horribly superficial humans are and worn a mask when he approached them or if Victor Frankenstein had agreed to create a companion for his creature (but left her without a functional uterus if he is really worried about his creatures having children).
Cry for the Devil: The last section of the book demonstrates that the Creature was formed by his surroundings, rather than born evil.
Ho Yay: Victor's describes Henry Clerval in a way someone would describe their love interest. Heck, his description of Henry is more thorough than those of his fiancée, Elizabeth. And he reacts to Henry's murder more strongly than Elizabeth's murder, too! When Elizabeth gets murdered, he is 'merely' heartbroken, much like with William. When he find out Henry is dead, he goes into hysterics and is bedridden with a deadly fever for 2 months!
It Gets Better: The first few chapters detail the back story of the sea captain who met the titular Doctor on his expedition to find the North Pole. If you didn't know that the novel was a Story Within a Story (Within a Story) you would read the opening thinking "Get to the unholy abominations against nature, already!"
There's a long segment where the Monster watches a family for about a year - his yearning for a mate comes from the young man being betrothed to an older woman from some exotic place, as well as his identification with Adam's desire for a mate in Milton's Paradise Lost.
Moral Event Horizon: Sad backstory aside, it becomes increasingly difficult to sympathize with the creature once he starts racking up the monster points by taking vengeance on Victor's innocent and completely clueless family members.
They Wasted a Perfectly Good Plot: Oh come on, a race spawned from the Creature and a manmade Bride would have been awesome. But, alas, Frankenstein had to destroy her body before she could be awakened.
Woobie, Destroyer of Worlds: The Monster, feared and hated by all and left to wander the world alone. So he kills people. Lots of people.
Uncanny Valley: An in-unverse example: Frankenstein explains that not only did he make the Creature out of dead body parts, he had to make him 8 feet tall to wire together all the smaller blood veins. The result is a monster that everyone is scared of at first glance, including the creature itself.