It must be said that this is rather more accessible than Foucault's Pendulum. Perhaps he had a rubbish translator this time round, so that the vocabulary is only slightly wider than is easily readable. Having not read any Cadfael novels, I'm missing comparative Detective Monks in the Middle-Ages ficton, but as an introduction to the genre it is certainly not bad.
Eco's penchant for semiotics and all that stuff don't come out too heavily. It's readable without an arts degree, although I'm planning on cribbing notes off the internet to understand the intentions. The main body of the book reads like a fairly standard detective story, albeit one that's slightly more complex than usual (and with an interesting number of plot-turns and events), but the ending is both a satisfying conclusion, and a glimpse into the deeper layers of meaning that Eco's embedding. The historical research (just like in Foucault's Pendulum) into the life of Middle-ages monks is pretty impressive, with the downside of showing up the main detective character as a Modern Man Using A Time Machine To Pretend To Be A Monk. Although I'm probably being a little harsh there.