Read the first page. Read it. See what it says? 'Dracula: a mystery'. That's what this book is! A mystery. Not The cheap, stereotypical story of the sort everyone thinks of around Halloween.
The Characters are intelligent. Stoker doesn't reveal everything at once. There are no peek-a-boo corpses or any other tropes designed to scare the wits out of you as a compensation for plot.
You're always wondering what happens next. It feels like Helsing and his friends are trying to defuse a bomb during the entire book. Dispose of the vampire before he decides to escape and sleep for another century or two. Dracula is cunning. Cunning, in the true sense of the word. Not the 'cunning' people use while reviewing movies (Though that's a bit ironic: I'm writing a review myself :P).
And it's free? That's just the icing on the cake.
I really don't like horror, nor do I like vampire stories. This book is one of the (less then five) exceptions.