
1) A lot of it is about physics and a lot of jargon is employed, since I only tangentially understood most of what was discussed, I felt a bit adrift.
2) It's set in a time-period that I know very little about; the fews years wedged between WWII and the paranoia of the McCarthy era, so again, I barely understood a lot of the vernacular and terminology used.
3) And this reason is related to the era as well, but I felt a lot of the dialogue was wrapped up in innuendo and subtly due the the fact that the main characters couldn't say what they wanted for fear of being spied on.
But I'm giving it 3 stars because I think that it's an interesting book which, although not comfortable for the modern reader, seems very well researched and considered. I also like the characters, by and large. I especially enjoyed Phoebe, a female physicist in the 40s (ooh! alliteration). She was gutsy.
It's not a romance, and perhaps I should've started with that statement. Sure, there are some romantic overtures and the couple you were rooting for does eventually get there, but typical it is not. I think the main things that I took from this novel was about the ridiculous and infective power of paranoia. However, if an object lesson does not interest you, then maybe this book is not what you're looking for.