Frankenstein is a classic for many reasons, some of which I will list: Stunning writing, pioneering plot devices, romantically sublime, elicits a ton of emotion, and asks the most poignant and lasting questions. 

It has it's own quirks, in that some of the book is quite meanderingly slow - from a syntactical stand point. It was written in 1812, you know, but then the plot pace is actually quite fast. 

I love Frankenstein, I love where it sits within literature, and I think Shelley was a genius. You will have a gutwrenching, tense, and doom filled time.