Well, it is not a Sci-Fi novel. If that was what the reviewers you saw were expecting, I can see why they might be disappointed. It was probably included in that genre because time travel is an important part of the story.
It is more of an historial fiction, with a love story that is central to the plot. It is very well-written, and one reason that everyone loves it is that the characterization development is excellent.
The love scenes can be a little explicit (and the adults are not always consenting) but they are important to the story and the characters, and no, they don't take up that much of the bulk of the story. So if story is what you are looking for, I think it's worth your while to give the first book a chance. There are 6 in total, with 1 (maybe 2?) more on the way.
If you are looking for a male perspective, here is what our guy Harvey had to say about the 'romance' parts...
Harvey said:
- I guess I have led a sheltered reading life, but I haven't read many books with as many love scenes as those between Claire and Jamie. I found those tastefully done, and interesting to read them from a woman's perspective. I think the fact that Jamie was inexperienced made those scenes more important to the story line and to understanding his relationship with Claire. I didn't think the raciness was there just for cheap tittilation; it was pretty central to the arc of the story.
Hope this helps.