I think it is. It's not a work of theology as The Pilgrim's Progress is, certainly, but Eco knows his theology and church history, and he gets it right in the book. I do think the book is rather anachronistic in lots of ways; Brother William of Baskerville often strikes me as a thinly-veiled copy of Sherlock Holmes rather than a Medieval Franciscan monk. But I suppose you have to sacrifice a bit of historical accuracy to make the story more palatable to modern audiences. (I did like the fact that in the novel Brother William was a member of the Inquisition; it gives him a bit of complexity in his character.) One thing I love about the novel is its investigation of the love of books not for the wisdom they contain, but as idols -- it's no accident that for all the to-do about the Aedificum and the books inside, we never get much of a glimpse as to what those forbidden books contain. Even with the Finis Africae, we only get hints. (Polanski plays the same trick in The Ninth Gate, a much inferior work that steals a lot from Eco's book). I also like Ellis Peters' Cadfael novels, which are rather like Medieval mystery stories but the eponymous Welsh monk Cadfael as the protagonist.