It was hard to read the beginning of the book - I did not care for Cora at all, not one jot. And it's always hard to care for a book when you don't care for a character.
I thought she was very VERY selfish. Hideously so.
But by the end of the book I found that I had started to care for her. I don't know when this started, because the character of Cora in the opening chapters was quite vile. But it was good that I had started to care for her - it gave the story more strength and showed that Cora had developed greatly as a character. It made my intense dislike for Charlotte and the Double Duchess stronger.
And Bertha is a great character, especially with Cora. I can't say I cared for her beau at all, but he was a bit of a prick, seemingly after only one thing. It was weird that the smart Bertha would want to be with him, but maybe he was the only one to see through the colour of her skin (or maybe that was the reason for his attraction).