***Note: this review assumes that you've read the book.***
One-sentence summary: Surprisingly low on real-time action, written in flowery-pedestrian prose, this book is still stunningly original, and I was pleasantly surprised to find themes on passion, marriage, and homosexuality that I never knew were there. (Or did I make those up?)
I haven't read any literary criticism of Frankenstein, so I may be way off the mark (or repeating something everyone else knows), but I thought the story could have been interpreted as a negative commentary on marriage as a soul-sucking, confining contract, and it had a ton of homoerotic content that I never knew was there. The whole piece seems like something very original for its time. The prose didn't feel special to me, but I think that must stem from the fact that it's sort of a "first" (is it the first?) in terms of being a horror novel, and from the fact that Shelley was so young when she wrote it. Perhaps because she had no one to model herself after, it's a bit rambling. In addition, the immediacy of the action is quite damaged by the fact that nearly all of it is narrated through dialogue and storytelling ("Let me tell you how I got here.")
Is ambition bad? The whole framing story--Captain Walton's discovery of the monster and Victor Frankenstein chasing each other near the North Pole--allows Shelley to introduce the premise that Victor is warning Walton not to allow ambition to consume him to the point where he destroys himself and others with it. And yet Shelley has Frankenstein contradict that message at the end of the story when Walton's mates and sailors want his guarantee that if the ice breaks, the captain will take the ship back to England in order to cut their losses. (That plan sounds reasonable to us, given how many people they've lost already). Victor, rather than the captain, rouses himself from his death bed to yell at them, "How can you embark on something you care so much about and then wuss out when it gets a little bit difficult?" (Obviously I'm paraphrasing.) Frankenstein berates them for not being passionate enough, for abandoning something that they once cared enough to risk their lives for. You could argue that Victor's death in the end proves that the obsession he's suddenly advocating for is unhealthy, and yet, he's only "alive" in the book when he's obsessed. Passion is, in fact, what Frankenstein seems to crave throughout the book, what elevates him from an ordinary existence to an extraordinary vitality. And the only time we see this passion in him is when he's inventing the monster or trying to kill him. He's mopey and directionless as a child and teen, until he discovers his passion at university. (By the way, the lightning-struck tree is only a metaphor for his understanding that science creates and destroys. It's never used in the process of creating the monster. It's only drizzling drearily on the day the monster is finished and comes to life.)
A commentary on marriage and family. On the subject of marriage: among Walton's first letters to his sister is the one praising his first mate's strong character. What story does he choose to tell? That the man gave up a fortune to foist his fiancee on another man. It's told as if the first mate was being generous (his betrothed loved another, but the other man was too poor for her father to consent to the marriage), but the undercurrent is clearly that this is a seafaring man who can't be tied down, and it's preferable to him to just hand over his lottery winnings, his land, and his living to the jilted lover, and talk his future father-in-law into accepting this new guy in his place, rather than to be locked in a marriage on land. There's no reason for this story to be in there except as a subtle commentary on family life, and how some men are not predisposed to it. Meanwhile, Walton himself is openly longing in his letters to Margaret that he wants a male friend--an intimate friend--a man "whose eyes will reply to mine silently." When he picks up Victor, his language about Victor's attractiveness in body and mind seems sexual to me; Walton uses words like "penetrate," and talks about Frankenstein in words we might expect him to use for a female lover, for instance, that "his voice is like music." Walton admits that he loses his inhibition too soon in the conversation and "opens his heart" to Frankenstein about his desires to have an intimate friend. I wondered as I read whether this odd sexualization was an artifact of the 19th-century language, but I've read a lot of Austen from the same era and she's able to convey the platonic relationship of her non-lovers without confusing me.
Did Frankenstein destroy his family? I think there may be an argument that Frankenstein has some sort of angry sexual fantasy against his cousin Elizabeth, and by extension his family life. He basically arranges it so that his best friend, his family, and his "cousin" (an orphan taken in by his family) who is sickeningly perfect and has been destined to be his wife since they were little, all get killed. He creates a being to do it. He is repulsed by the thing he has created, but runs from it rather than kill it. He fails to tell anyone that he saw a giant, a monster in the woods where William was killed, with the feeble excuse that no one would believe that he had created it--but why does he have to say he created it? Why couldn't he have reported that he saw the thing near the spot where William was killed? He literally allows Justine to be hanged. When Elizabeth is murdered in the room at the inn, while Frankenstein supposedly waits to confront the beast outside the door, Frankenstein inexplicably freezes rather than burst through to save her. He waits until the second scream, and by that time she is dead. In terms of language, when Frankenstein talks about Elizabeth and her family, the passages are dull, almost unbearably so, like a bad pastoral painting. But these passages feel deliberately dull and unbearable to me. Victor uses the same language over and over again about their "amiable countenances" and his "excellent father" etc. These are platitudes, and deliberately flat, while the descriptions of the monster are vibrant, raw, and exciting.
Homoeroticism. In the end, the passionate interchange between Frankenstein and the monster as they chase each other across the tundra is so charged, it feels almost like the death scene in Romeo and Juliet when the monster is finally grieving over the dead body of his "lover." He kept Victor alive for the chase, and he has nothing to live for when he's gone. Gradually, the monster had pared all his desires down to the lust of being pursued. For his part, Frankenstein's passion for finding him and killing him border on the obsession of a lover.
I suppose you could interpret some of this as the obsession of a child for its parent (and the monster wanting his "father" to pursue him) but the lack of interest Frankenstein showed in starting a real family of his own sort of negates any analogy to parenting on his end. He shows almost no emotion over Elizabeth's murder. It's turned instantly into obsession for the monster, with some token comments about how the monster has guaranteed that he'll live a miserable life.
Construction of the novel. I thought the world-building was a bit weak, but perhaps understandably so, given that it was such a "first," and that Shelley is much more interested in the themes than in the sci-fi. Interestingly, I thought it was clear that Frankenstein "grew" the monster rather than "build" him from spare parts, as the movies have interpreted. He does make many trips to the morgue, and he robs graves, but he's very clear when he says that he did that to understand human anatomy and biological processes. He uses his handy dandy chemistry set to grow the monster (and takes that set with him to the Orkney Islands, where there are no cadavers, to build the bride). It showed Shelley's scientific naivete that she made the monster 8 feet tall with the excuse that building the "minute details" of the monster was so difficult Frankenstein chose to do it on a larger scale. It shows that she doesn't understand that an 8-foot person would simply need MORE capillaries and cells, and it would require more work! The monster's exceptional physical abilities are never explained. The way he taught himself to speak and to read was lame (did the people in the cottage really use the word "expostulate" in their ordinary conversations with each other?!). It was a stretch that he could rise up from the moment of his awakening, look in on his creator through the window, and walk away, but then had to learn everything from scratch in the woods like an infant (even as far as distinguishing what light and "seeing" are). There were a lot of coincidences. Here's Victor visiting the site of William's death because he can't get past the locked city gates...and there's the monster scaling a cliff! Here's the monster, wandering the woods after killing William...and he stumbles on Justine, sleeping in a barn! Here's the monster, wondering about his ancestry...and what's this journal in the pocket of this coat? Why, it's Frankenstein's scientific journal, detailing the monster's creation! The monster dumps Clerval's body on the shore exactly where Victor washes up in his boat, etc, etc.
In sum. The modern horror genre has evolved a bit more in paying attention to world building, and in telling the story via a narrative that imparts some of the excitement of the tale. But Shelley's foray is original and thought-provoking, even two hundred years later. You can't ask for more.