Eli Bendersky's website As you can guess from this pre-amble, the book is very good. I'll magnify this - the book is excellent. Definitely one of the best I've read, at least in some time.
It's hard to mention anything from the plot without spoilers, so I'll just explain what I liked about it - that it has the two virtues I love most about non-fiction books.
First, it is very readable. A page-turner, as some call it. The plot is so exciting that you just can't put the book down. The "Just one more chapter" syndrome hits hard. The author doesn't spend time using overly fancy language, present un-needed characters, etc. Everything is clear - the characters are well built and fit their roles precisely. The feeling that there is a great mystery you don't understand, and almost every chapter reveals some parts of the puzzle is enthralling and you just can't stop reading.
But high readability is also a virtue of some authors, whose books "fly through" but feel empty once you've read them. Read another couple of the author's books, and you feel it's all the same thing, and you didn't gain anything bar some entertainment time.
And this is my Second point: "The Da Vinci code" is different. The book is full with interesting information, and general knowledge about history, symbols, religions, riddles, etc. Naturally, some of the (more speculative) things may be innacurate, but there are all the reasons to believe the historic facts. I personally learned a lot about Jesus Christ and the history of Christianity (don't let this scare you, the book presents quite agnostic views, but the history of the great religions is still very interesting), and even about art (especially Da Vinci's).
The book has some weak points, but they are negligible comparing to the good points, so I don't feel they're even worth mentioning.
In short: highly recommended