I read all the books over the summer and have just reread Voyager, so I'm back with the show iyswim. The time travel thing is a bit annoying, but Claire tells Geillis that she thinks it's because she focused on someone each time, Jack Randall, Frank Randall, Jamie... Geillis uses gemstones and a blood sacrifice to get more scope and be able to travel further than the 202yrs. Roger almost stuffs up because he thinks of his father and you can't cross your own time line. I think, but DG does seem to be adding to the rules with each book 
.
I do really like the books, as they combine lots of bonkers adventures, but add a certain amount of grounding with historical, medical facts (though, they could bear substantial editing, as shown by the screenwriters 
). I like the portrayal of Jamie and Claire 's relationship with a fair amount of it not always running smooth. I think a lot of stories set in the 1700s with redcoats, pirates, outlaws etc. can overly romanticise the time period, but these don't and you can see that life was very tough and brutal as well as exciting and adventurous. They kind of remind me of the Anne Rice Vampire Chronicles, especially Voyager with the plantations and voodoo in the West Indies, with the you don't know what will happen next, violence, adventure, sensuality, history etc.
I also agree with the Roger and Bree stuff, it just feels wrong in later books, to read their sex scenes after reading those of Bree's parents. Though, the show seems to be making Bree more sympathetic rather than fiery.