A classic first-contact novel, and Flynn displays tremendous talent for creating (and gets readers to really grapple with) characters who live in alien paradigms. That's actually a primary reason for my love of this genre. Oh, sure, I like the evil-conquest-blow-shit-up-War-of-the-Worlds stuff. But the real hook comes in the more anthropologically-oriented approaches. What would it mean to be in this kind of body, on this kind of world? These kinds of novels seem to wrestle that old philosophy conundrum about how bats see the world, and in imagining the alien they in the best examples gloriously estrange us from our common-sense understandings of the human. (Ursula LeGuin's work is the gold standard here.)
For _Eifelheim_, it's paradigms, plural, because the book's central conceit is an alien craft crashlanded in 14th-century Germany, and we readers must (with great pleasure) untangle the priest Dietrich's scholastic Catholicism and natural philosophy as often as we do the culture and consciousnesses of the grasshopperish Krenk. The most amazing accomplishment are those passages where Dietrich's struggles (with his faith, with his scientific theories, with his dialectic engagement) seem genuinely insightful, rather than the cartoon superstitions we often attribute to medieval thought. As a novel of ideas, it's a winner; better yet, the novel embodies such ideas in thinkers and a vision of communal life, avoiding the airlessness of abstraction.
The book might get a higher rating if Flynn had avoided two things. First, a venal sin, there are moments where Dietrich engages with some Krenken insight, some bit of their science collides with his own worldview, and he leaps to name the insight and uses a term we 21st-century readers recognize readily. (E.g., in discussing the elements of information employed by the ship's computing system, Dietrich imagines calling them bits or bites....) Cutesy, and unnecessary, and popped me right out of the narrative.
But a far more mortal offense is a contrapuntal narrative set in the present-day, where a Bickersonian couple--she a physicist grappling with multidimensional space, he a cliologist (yeah, yeah) trying to make sense of the disappearance of a medieval German town--argue in an ostensibly screwbally manner, grapple with their own paradigms in ways that are meant to echo the 14th-c narrative, and generally pissed off this reader every time they apppeared and interrupted. While Dietrich and the Krenk Hans were embodied, complicated, challenging characters, Tom and Sharon were thin gruel. I found their technical jabber not just too technical but too jabber; I found the jokey tone and use of humor at best forced and at worst insufferable.
So the novel is more of a mixed bag. I'd have given the 14th-c narrative four or five stars, but I'd never have read past page 30 of the 20th-c narrative, and it'd be one-star; luckily the latter comprises only about 1/10th of the whole novel. If you grit your teeth and barrel through those sections, it's a pretty damn good novel....