It's fair to say Brown is a controversial author. He has an extraordinary way of advancing the story, leaving you hanging for more at the end of every chapter. On the other hand, he's been criticized of poor literary value, and his characters seem a bit shallow. It's always the athletic professor and the smart, strikingly beautiful woman scientist in her thirties (probably reflecting Brown's own marriage). Basically, it seems like he's writing movies in the form of novels.
Dan Brown's books are always full of interesting facts and descriptions of locations, clearly showing the background research he's doing. Personally I like it very much, it gives credibility and realism to the story.
On the other hand, in this particular book, Brown is surprisingly ignorant regarding encryption technology and data security in general. He keeps mixing 64-bits with 64-bytes, and his view of computer viruses is similar to the movie Independence Day, where the extraterrestrial aliens were conveniently owners of Macintosh computers ready for Jeff Goldblum to crack... You can find a lot more of these on the net.
Anyway, if you (like me) are willing to forgive the weaknesses, Digital Fortress is a pretty cool read. After reading it and Da Vinci Code, I'm certainly going for the rest of his novels. In fact, I just started his second one, Deception Point, which seems promising so far.