Interesting that he describes the first hundred pages as a penance or initiation for reading the novel. I found myself skimming much of the historical facts about the sects and heretics. Is all that detail really necessary? Isn't it enough to know the facts without so much detail? I would certainly cut a lot.
And it seems that the author added the extra levels of narrator (a modern translator at least twice removed from the young novice narrator) as a salve to his own ego. Odd.
But at it's core, there is the traditional detective novel, much like a story of Sherlock Holmes narrated by Doctor Watson. William of Baskerville is the "detective" and everything is narrated by the novice Adso.
Much of the extra material valued so highly by Eco was, of course, removed for the movie.
Link to Amazon: The Name of the Rose: including the Author's Postscript