I think you've got a problem with story telling when most of your dramatic tension revolves around attempted rape or rape. But in the case of Outlander - the guys probably get it worse. I think most of the rape against women turn out to be attempted whereas the guys who get raped are...well...concluded.
So plot: woman gets sent back in time by walking through some standing stones. She is thought to be spy, eventually forced to marry an outlaw highlander, they fall in love, he gets raped and beaten by the ancestor of her husband back in the future. She manages to drag her highlander husband back from the brink of death. Presumably in the future they try to stop Bonnie Prince Charlie's war.
But MOST of that is like in the last 100 pages. IT IS 862 PAGES LONG OF VERY LITTLE HAPPENING. There's a lot of horse riding, dinners, walking around, shagging, screaming rows between the newly married couple, a few more attempted rapes and a lot of frankly boring family history.
I was sitting there around page 400 going WHY WOULD ANYONE READ THIS? But then I thought, well, it's basically violent Downton Abbey but with burly men in kilts. No wonder it's now a television show. Less maids, more men without shirts and wearing tartan.
It's not bad but I don't think it's worth the 862 pages of effort. Lots of the women are quite strong characters, so I think it passes the test. The lead female character, Claire, was an army nurse so she's a more than competent healer in the 18th century.
BUT IT'S SOOO BORING. Oh my god is it boring.
AND WHO WOULD NOT GO BACK TO THE FUTURE? Sure, your new highlander hubby is all good in the sack, but he could die next year from blood poisoning or a sword to the gut. Or from Jack Randall (the rapist with a taste for the lads) who is just unbelievable as a character. Like honestly, I think at the end it basically infers that he also probably raped his younger brother. Eww.
Claire also has lots of bouts of forgetting about the 3 or 4 attempted rapes, the lots of up close and personal killing of people (though she does a few of her own and thinks relatively little of it) and the near getting burned to death as a witch. WHAT. WHAAAAT. I would have been all "it was totes fun Jamie, but fuck the 18th century. I'm going to go back to showers, antibiotics and lack of people trying to kill/maim the people around me all the time."
So yes. I think it gets a 3/5 because it's not as awful as other books I've read from the list. It's at least internally consistent and I genuinely like Jamie and Claire. Also, I gave a lot of the other crap 3/5 and it's no worse than Assassin's Apprentice or Ringworld. My personal recommendation would be to watch the tv series because it's probably less effort.
ALSO OMG THE LOCH NESS MONSTER MAKES AN APPEARANCE. Fuck that.