You're entitled to your opinion. I agree that Kathryn Winnick would have been a better Cassie Dewell though I thought she did fine as Jenny.

Maybe I like the idea of the story in the series because I found Box's portrayal of the older sister far less preferable to the one that we got in the series.

And I admit the series completely shifts away from the book plot in the first case. Still that's why I tend to not read the source material of any show or film until after I've seen at least one season. I don't want it to prejudice me one way or another. That said, I will concede if I had read the book first I would not have wanted to see Big Sky in the first place. My perspective and you are free to yours.