I read the review of Simon Blackburn trashing the book: Eco made a few mistakes concerning the two dogmas of empiricism (he confused Davidson's work with Quine's first dogma). So I am sure many readers hesitated after a review by such a rigorous big gun thinker as Blackburn.
When I started reading the book I was taken aback by the combination of depth and the vividness of the style. Eco is sprightly and alive, something that cannot be said of many philosophers dealing with the subject of categories.
The notion of categories is not trivial: you need a simple conditional prior to identify an object; it is a simple mathematical fact. You need to know what a table is to see it in the background separated from its surroundings. You need to know what a face is so when it rotates you know it is still the same face. Computers have had a hard time with such pattern recognition. A PRIOR category is a necessity. This was Kant's intuition (the so-called "rationalism"). This is also the field of semiotics as initially conceived. Eco took it to greater levels with his notion of what I would call in scientific language a compression, a "simplifation". This leads to the major problem we face today: what if the act of compressing is arbitrary?
Not just very deep but it is a breath of fresh air to see such a philosophical discussion nondull, nondry, alive!