I don't know what can be said about Cousin Bette that hasn't been said over and over again. Critics love it and hate it and the reason is because the characters, though mashed together somewhat haphazardly are powerful, intriguing and thoroughly flawed. When Paris is the background of a novel, we know that good people will die, bad people will prosper and innocent bystanders will be trampled underfoot. It is the Parisian way... or at least it is in novels.
For me, the joy of not knowing what will happen was great in Cousin Bette. I didn't know which characters would live or die, whether virtue or vice would save the day, or if the day would be saved for anyone. The ending is perfect. As in real life, no one learns a damned thing (except of course the reader). My admiration for Balzac went through the roof.