What do you think is the most well-known story written by Robert Louis Stevenson? Treasure Island or Kidnapped are certainly much loved and widely-read, but I think The Strange Case of Dr Jekyll and Mr Hyde is better known. In fact, there's a good chance you've never even read it but you know the story. Wikipedia says there have been over 100 film versions alone of the story although the one I remember most was Bugs Bunny (actually that probably doesn't count as a "film version"). And it's because of this that everyone already knows the basic storyline that made it one of the most disappointing books I've ever read when I read it over 25 years ago. (And let's not forget the classic 80s song by Men at Work.)
One aspect of Jekyll & Hyde that I found interesting, however, was Jekyll's reason for doing what he did. He felt guilty over his sins and shortcomings, and wished he could separate his sinful side from himself (or that self he believed himself to be), thereby freeing himself from the anguish and guilt of his weakness. Unfortunately, it didn't work out like that. Instead, Hyde was unleashed and part of Jekyll enjoyed the indulgence of Hyde's immoral activities. And the more Jekyll allowed Hyde to run free the harder it became to control him, until Hyde was becoming the controlling force within him. Of course, this was a common caution preached from pulpits everywhere upon the release of the book, but it's not a part of the story we ever see or have even come to associate with it. (Not in the Tweety Bird version, either.)
At any rate, it's a short and easy read and the concept of inner conflict is an interesting aspect of the story (and it's the only book I could come up with that is somewhat Halloween-ish). I recently listened to the audio version and it's more enjoyable when you understand how the story is written and aren't expecting a surprise when there isn't one.