What can I say? If you think about this and Pride and Prejudice as being completely independent – different characters with the same name etc, then you might just like it. If you can’t do that, then you will hate it (and rightly so – Darcy does not have a hired thug who does his dirty work!).
The best I can say is that it’s not bad as a trashy regency novel – no where near as good as Georgette Heyer, but I can see that a bit of research had been done. Although as Austen did say
while Mary obtained nothing higher than one of her uncle Philip’s clerks, and was content to be considered a star in the society of Meriton
Taken from  A Memoir of Jane Austen
I’m not sure why McCullough felt the need to alter the story.