Victor Hugo's 1,232-page story is so much better than the musical or the movie. I drudged through the first hundred pages (and still got lost countless times throughout the rest of the novel) but eventually made it through. But I loved this book so much because it was thorough--I mean really, really thorough. There are about 200 pages talking solely about Jean Valjean's voyage through the sewers while he's trying to save Marius. That was pretty tough to get through.
But even though most of this book is so detailed it hurts, there's still a great story underneath it all if you're willing to take the time to analyze it. Even though I basically watched the movie on repeat, I picked up on so many more things after I read the book. And since the book is so detailed, there's so much more information in it. There are many connections between characters that I would have never realized if not for the book. Also, there are some really magnificent quotes, like in the very last paragraph of the book:
Should we continue to look upwards? Is the light we can see in the sky one of those which will presently be extinguished? The ideal is terrifying to behold, lost as it is in the depths, small, isolated, a pin-point, brilliant but threatened on all sides by the dark forces that surround it: nevertheless, no more in danger than a star in the jaws of the clouds.
So if you're a huge Les Miserables fan like myself, I definitely recommend taking the time to get through the original novel. It may take you years (like me), or if you're lucky, it'll only take you a month or so. Either way, Victor Hugo's genius definitely shines through in this story, and will only make you appreciate the movie and musical more!