Victorian novel, so of course it's a long one, but it's also sensationalist fiction, which makes it fascinating reading.
I'd read Wilkie Collins's The Woman in White whcih is the other great Victorian sensation novel, but I think this one was better crafted. I especially liked that the villain in this one was a woman, but because a woman also wrote it, she is portrayed as a criminal without all the misogynistic Eve-spawn crap that most men (at least in the Victorian and earlier eras) wrote into any depiction of evil women. I actually rather admired Lady Audley at times, even though she was a horribly spoiled young woman who could not be content to live with the decisions she's made in her life (the limited nature of those options in the society depicted does somewhat mediate this problem, but she still takes the lowest road possible).
I read Collins in a Victorian lit class, but I think if I wanted to include a sensation fiction novel, I would include this one rather than Collins, just as I would replace Rushdie as a representative postcolonial writer with Zadie Smith.