I've read all of Dan Brown's books and this seems to be his weakest. The plot is predictable and if you know at least a bit about how computers work, you have to turn off your brain in order to enjoy the book.
Still, Brown knows how to entertain a reader and if you ignore the books shortcomings you'll come to enjoy the book's "roller coaster" style. "Digital Fortress" is also a good and exciting introduction to cryptography, and that's a plus in my book.
Sure, this book is literature's equivalent of an action movie, but it's one of the better ones.