First read this ages ago (I think during a summer/winter vacation in either college or high school?).
It's such an oddly structured book! Ok, it's not that odd, but it goes against your expectations, if you go in there thinking that Dr. Jekyll is going to be the main narrator. This is basically a mystery/detective story; you don't hear Dr. Jekyll explain things in his own voice until the final chapter.
And boy oh boy is that final chapter a doozy. It's extremely allegorical; you end up underlining nearly every single sentence. The Jekyll/Hyde divide can be interpreted in so many different ways: a metaphor for addiction, an exploration of the Jungian "shadow" archetype and other Jungian ideas (how we are always presenting a "mask" or persona to the rest of society), Freudian theory about civilization and repression, Shakespearean themes re: how Jekyll's tragic downfall comes about because of his ambition and vanity, etc. (It's interesting to think about a lot of people think the "Dr. Jekyll/Mr. Hyde" divide is about "good vs evil," but the book makes very clear that Dr. Jekyll already had debased qualities that he was repressing, and which the Hyde persona allowed him to fully embody).
Anyway, there's a reason why this book has entered the realm of myth—it taps into something really powerful and elemental. (It's also a bit Jungian how Stevenson says he came up with the story after a dream!).
It's v. interesting and Victorian how the book never specifies what were all the evil, debased activities that tempted Dr. Jekyll, and which he fully indulged in as Hyde. I was dying to know!! Drinking lean and trying to organize threesomes with underage girls in the club...? The fact that the book doesn't go there allows you to invent some real perverted things in your imagination. You just know that Edward Hyde was reppin' for that low life....