I can't speak for others, or those that have read only the abridged or modern translations, the following is my personal opinion based on a reading of an old translation from the French done in the late 1800s (date uncertain, old oil skin book found through a dealer in London). Throughout the double volume, the story is a treasure of great lines, mostly from the Count after he begins to pursue his old enemies. These include the famous "Wait and hope!" line that makes the whole ending worthwhile. The Count's view of humanity is sharp and penetrating, though you do have to suffer through some long passages in the second book to find them. Remember the scene at the gallows where two men were going to be executed, and the fuss that occurred when one, the Count's man, receives a last minute pardon, there is a great line there on the real nature of mankind. The revenge theme is a vehicle for rising above such, a struggle the Count goes through constantly. I could go on for days but briefly, this is my all time favorite novel. You should really try to read it in the original French or an old translation, most modern translations butcher it horribly. There is an old great Japanese translation also, which may be even better than the original or the old English versions!
A real classic in any case. That's its appeal.