First of all I must say that this book is huge! 1000 pages, relatively large, with small font, it must be one of the longest books I've ever read. I read the full version, because I don't like abridgements. Truly, there are extremely long books (this one included) which won't be spoiled by a bit of cutting, but I just don't like that someone else decides what I read or not.
This book is rightfully considered one of the greatest novels of all times. It spans a period of a few years in the life of Jean Valjean - an escaping convict who "switched to the good side", and the characters around him. The place is France, mostly Paris, and the period is the first half of the 19th century - a very turbulent times in Europe and France in particular.
Victor Hugo certainly writes beautifully, his command of the words and sentences is excellent, and the philosophic detours, though tiring at times, are very touching. I hope not much was lost in the translation, but even in English I felt the power of words under Hugo's pen very well. The level of English is quite difficult - I'm not used to looking up words in the dictionary, but with Les Miserables I was forced to do it quite a few times.
This is a book about everything - right and wrong, love and hate, war and peace, goodness and evil, rich and poor. The characters are very believable, and in fact developed extremely well. Hugo doesn't just throw random characters in, any one has his place, and is described sufficiently well for the reader to relate to him. This is true about other facets of the book as well: although being very long, you won't find needless things in it. Everything has a reason, and Hugo knows how to collect facts and bring them together in a masterful way, sometimes surprisingly.
I especially felt for the descriptions of poor/hungry people in this book - extremely credible. Reading the book makes you actually feel sorry for these people, specially children, relate to their hardships, and being thankful to have a roof above your head and food in your stomach. It's also amazing how strong some of the characters are. Eponine, Gavroche, Father Mabeuf - young or old, these people have been beaten by the sufferings of life enough to develop certain power and a way to look life right into the eyes - something to admire.
The main message in this book as I see it is living with your conscience. What is really to a person is not what others think of him and how they judge him, but what he feels about himself, his inner peace of mind. Jean Valjean was certainly very hard on himself, even after doing so much good. I even felt that he's a bit too much self-criticizing, but the moral is clear - you can run from the police, hide from people, but you can never escape yourself.
It is curious that I didn't find any character to relate to - any "favorite" character. Even Jean Valjean, the most obvious candidate, is so much introverted, that I as a reader felt some distance from him.
There were also some things I didn't like about Les Miserables, but compared to he positive things in this book, they are minor. One is "the detours", usually historic like the battle of Waterloo or the sewers of Paris, or political, like the whole discussion of revolutions before the barricade scenes. Some of this are just too long, and in this case I can relate to the abridgers. Hugo certainly wants to deliver a lot through this book, and sometimes he goes off the limits of a novel. The other is the coincidences. There's just too many of them, IMHO. The main characters in the book just can't stop from running into each other, especially Jean Valjean, Javert and Thenardier. It keeps the plot moving, but it feels a bit forced at times.
To summarize: this is a great book. Prepare yourself to spend a lot of time reading it - it's long, the language is difficult and you have to be fully awake, or you'll easily miss key moments. But it's all worth it, this book is a literature marvel, I enjoyed it immensely.
Edit (30.07.2010): I've just finished re-reading the book and liked it a lot again, so I don't have much to add to this review. One minor issue is that while reading the last few tens of pages I became quite annoyed with Marius's hypocricity towards Jean Valjean. Marius, who fought on the barricades against the government, killed gendarmes and soldiers, and would surely be hanged it he'd be caught, was just terrified and appalled by Jean Valjean, the past convict who was in the galleys? Give me a break.