I finished this a week ago, and I've had trouble coming up with a rating or a review. I usually like Gabaldon's writing for the most part, but this book was a disappointment. I think I've got to go with another 2-star here.
It's obvious that she did her research, but a lot of stuff seems to just be thrown in to get to show off said research and didn't make a lot of sense plotwise. In fact, I found many passages to be confusing in this installment, and many others were just plain dull and didn't seem to serve the story. I agree that she was using too many viewpoint characters in this one. So we have a looooong book with random stuff happening across different times, but very little is actually accomplished...including a satisfying ending. There were several cliffhangers left unresolved, and the book just stopped rather abruptly.
I thought the book before this one was getting better, so Echo seems even more lackluster by comparison. Claire & co. get swept along by history, but I wish they had a bit more agency and weren't just floating around like flotsam. This is an obvious bridge to the next book that doesn't stand alone as a satisfying novel.