Being a massive fan of the original novel, I couldn't help but feel betrayed by the show.
I liked most of it, so I might aswell share what I disliked - the portrayal of Sir Percival Glyde, and partly Count Fosco.
Making them both sexual deviants is simply unfaithful to the original novel, Glyde seems utterly repulsed by the notion of physically interacting with his wife, nevermind ravaging her the way she does in the show.
For Count Fosco it is maybe more believable, but the add sexual assault where it needn't be there to make villains all the more dislikeable is simply lazy writing, and I do not believe the book itself implies such a thing would occur.
Atleast it isn't the Lloyd Webber portrayal.
Tldr: SA adds nothing to the plot.