I enjoyed NOTR -- although full confession that Foucault's Pendulum* is far and away my favorite Eco, NOTR is a close second. Like you, I enjoyed the theological aspects and I found myself really enjoying the historical religious minutia. Depending on the version you've got, there's an author's afterword where he writes about writing NOTR and how he found himself writing in a century/setting that was not the one he was most familiar with, due to logical constraints within the story, and that he intentionally made the opening hundred pages or so intentionally difficult to get through.
* As far as I'm concerned, the only negative thing that can be said about Foucault's Pendulum is that typist Dan Brown got "inspiration" from it for his typing excercise Da Vinci Code.