In reply to DaveHK:
Been a good few years since I read them, so the following is a bit vague but:
Name of the Rose is by far the best, the main story and the historical interjections are both very good. I've re-read this book several times and still enjoy it, despite knowing the ending.
Foucaults Pendulum is less well crafted as a story, but the historical bits about the Templars are still great. It starts well but tails off - like someone said, it could have done with a bit of editing. I suppose it does come across as intellectual, but then it was written by one, so it's hard to hold that against it. I'd put it as a tied second with...
Baudolino. Again, I have memories of the main story tailing off and it is nowhere near as good as the Name of the Rose. The historical bits are the best bits again.
I struggled with The Island of the Day Before.
In conclusion I'd recommend reading NOTR despite having seen the film.