Frankenstein, or The Modern Prometheus
I can see why this book might be tedious to some people, especially people who don't enjoy wallowing in emotions. But me, I love a good wallow. I also love that this book was written by an eighteen year old girl. H.G. Wells gets most of the credit for inspiring the modern day sci-fi genre, but it was really Mary Shelley who started it up for him in the first place.
Like most books I read in high school, I enjoy it so much more now that I'm an adult. It was a bit hard to get into at first as the first twenty-five pages just kind of jump into the middle of this guy's letters, but by the end I could appreciate the perspective the three different narrators (Robert Walton, Victor Frankenstein, and Frankenstein's monster) lent to the thing. Nowadays, we probably would have done away with the framing device of Walton's letters, but that sort of thing was very much "in" when this book was published.
It's funny that I've seen probably every permutation of the Frankenstein story, including Young Frankenstein, Bride of Frankenstein, etc, and homages like Edward Scissorhands and The X-Files episode "The Post-Modern Prometheus" when I could barely remember the plot of the original all these years. It's nice to have this under my belt. And man, it really is just a sad, sad book.