I wouldn't blame lack of history for your problem, Intensity, this book just seems poorly constructed and written.
I loved Wreck which was a masterpiece, and was really hopeful for this. Also when he read the small part of Eifelheim, it sounded good. Love the idea of aliens and history.
At the end Flynn says in one of his notes that he had a hard time trying to write as modern person, from the medieval perspective of the people in the historical setting. It was evident in his writing. So much of the early part of the book was just the equivalent of white noise, and was unremarkable and unmemorable.
That self-consciousness, where he couldn't just write the story from the within the characters, without worrying about the accuracy of the historical voice produced an awkward stiffness that was there for 3/4 of the book in the medieval section, and that was the only decent part of the book.
It wasn't until almost the end that he seemed to bond with his characters, and the story actually started to flow. He got out of the way, and let them speak. Hans and Dietrich managed to shine, but the many of them were mostly lifeless except for being pretty stereotypical medieval people.
The modern part was just a waste in terms of story (even though it was the original genesis of the idea). The two main characters were nasty and unsympathetic. Worse they were clearly fake constructs, just to do a running science info dump. There was no real integration of the two stories, they were just pasted together. Flynn throws out the idea that the development of self-exploration in philosophy/religion/psychology is due to a mistaken understanding of advanced physics that humans took to be a metaphorical reference. He never expands on it, which if he had done in the modern section might have tied them together better.
Flynn didn't finish anything in either story. He just left once he revealed his punch line. What happened to Dietrich, did he die of plague (not a given with the recently discovered gene mutation), or was he finally caught and punished by the Church for his past or new sins ? Why was the village never resettled ? Ghost stories lose their potency over 700 years; did other things happen later on ? Since the plague was so devastating, how many people were actually left alive to know/spread/believe the ghost stories in the first place ? How was this location any different than many others in the Black Forest with equally fearsome tales ?
That Dietrich was a scholar and a man of reason and just happened to be there, along with the various exotic human visitors to that small spot on the road seemed to be just too much Deus ex Machina. Even with all the dispersion due to fleeing the plague, it stretches credibility.
In both sections of the story there were way too many foreign languages being used, words and phrases and no translation, glossary or footnotes. Almost as if he wanted to make the humanities portion of the book as obtuse as the science. That Tom and Sharon carried on in various foreign languages was just a slap in the face to the reader, because there was no reason for it. At least the medieval section had a reason to use German and Latin.
I don’t think Flynn did enough to explore why Hans and the others stayed when their craft left. I thought it could have been interesting to see what motivated Hans, what Dietrich assumed to be reason, and what minor factors also played a role.
What I did like was the interaction between Hans and Dietrich. It was awkward at first when Flynn couldn’t quite express himself, but it got much better, and eventually became the best part of the book. Hans was less alien than some of the humans.
I also liked the dying sheep and other large livestock, not just the rats. He seemed to be incorporating the theory that some of the death from disease was actually Anthrax and not just plague. Neither Bubonic nor Pneumonic plague explains those who were healthy at night, showed no physical symptoms and were found dead and unmarked in the morning.
It took me a while to read it and when I was doing so, for most of the book I just wanted it to end.