The Island of the Day Before, Baudolino and The Mysterious Flame of Queen Loana felt more like he was trying to test you, in each of those books, to see if you are worthy of consuming the entire book. Every time you feel you have a reasonable grasp of what is going on, he'll descend into a phase where you'll be lost again.
The Prague Cemetery, on the other hand, was utterly fascinating. Really enjoyed it.
Perhaps not even Mr. Eco is immune from repeating clichés.
http://umbertoecoreaders.blogspot.de/2007/11/postscript-to-n...
You are of course right that Eco pushes a number of the same buttons that Brown does, yet without being ridiculous.
The same could be said of Dostoyevsky. Those long, drawn out passages are often there to make a psychological impression upon the reader rather than adding anything to the plot line per se.
Though at times it did read like a database dump (albeit a fascinating one), the intricacy of the background of theories and history is all in service to the ridiculousness of the plot. Without it, the profound stupidity of the formulation of the meta-conspiracy would not have been believable.