For my own self, me that is, personally.......I read three of them and they teetered on the edge of the Tripe Chasm.
Bits of them were REALLY good, but I could not "get" the hotness of the 18th century Highlander who was the "male lead". Unfortunately the description of his person nearly exactly matched that of my cousin Donald, and my cousin Donald is about my least favourite guy in the known universe.
Having said that, I repeat: bits of them were REALLY good, since there is a Time Travel element to the story. This is NOT a spoiler, btw, or if it is, it is a very minor spoiler.
Ms. Gabaldon, we are told, did a lot of research on the Jacobites, and Bonnie Prince Charlie, etc., and I guess she must have as she did not make the kind of egregiously stupid mistakes so many writers make when writing about that era.
The Outlander series is sorta like Jean Auel and her Earth's Children series, which I toil through religiously even though they are AWFUL, particularly the most recent one. I am more than half ashamed of reading them, but I confess I am waiting for the very last. I do expect that Ayla and Jondalar will build a nuclear power plant and develop faster-than-light travel, this time.