1. The subject wasn't just not original, it was lazy.
It's like Dan Brown rewrote the Cliff's Notes for Foucault's Pendulum and took out the interesting parts of it. I loved Foucault's Pendulum because it did what I want books to do for me. It entertained me and challenged me and made me desire to learn more about a subject (in this case, the Crusades) without making me feel like a moron for not knowing as much as Umberto Eco.
2. The writing was horrible.
Everything writers are told not to do, Dan Brown does in spades. Except that rather than coming off as some kind of edgy experimental fiction, like the use of second person in Bright Lights, Big City, it just comes off as what it is - bad writing. Brand names used as shorthand for description, lazy cliches, more adverbs than you could fit into a college freshman creative writing project.
3. The most poorly developed characters I've ever read in a commercial novel.
Supposedly this is a story about a woman who is a crack decoder helping a man who is a grail expert solve the mystery of her uncle's death. Except that, if you've been paying ANY KIND OF ATTENTION, you've solved that mystery after the third chapter and the rest of it is just one long cringefest because what was obvious to you 100 pages ago still hasn't dawned on these two "experts." Any text that claims that backward writing is an undecipherable code assumes that not only are its own characters morons, but that you are too.
4. Every time I hear about the popularity of this book, I am reminded of the low mentality of the vast majority of the country, and that depresses me.
The worst part is that I bought it too. It was the first audiobook I got when I got Audible, and I waited for the entire 15 hours of it for it to get good. And once I was done and realized that I had been had, I called everyone I knew and told them "Don't read this! It's terrible!" And my family being what they are, they all rushed out to buy Foucault's Pendulum. That was gratifying, but I realized that my family was in the tiny, tiny minority. There are people out there who have read the book and now feel smug and cool because they think that they've been let in on some secret. But it's like tasting McDonald's food for the first time and being smug because you've been let in on the "secret" that their secret sauce is Thousand Island dressing. When Umberto Eco's book is like the most amazing meal a person could have.
I would be happy to lend anyone who wants it my copy of Foucault's Pendulum.