After reading DaVinci Code and accepting it for what it is (a story, not a 100% factually correct account) I ordered Digital Fortress.
A collegue at work warned me that reading these books "the wrong way round" would be dissapointing, and he was unfortunately correct.
Both have an American academic jaunting across Europe like a CIA field agent, in search of something they do not fully comprehend while some sinister world organisation (in one, the NSA, in the other the Church) pull the puppet's strings. And both have a physically impaired assassin out to hamper the whole thing.
The characterisation is shallow, such as the depiction of the NSA workers by phrases like "...he knew she was right; Ms X's instincts were infamous for always being right..." which doesn't create any reader empathy - in fact it makes you wonder how they didn't avoid the whole crisis in the first place it they were all so perfect!
I think Dan Brown has a random plot generator:
<insert main charachter's name> is an academic with language skills, sent to <insert European city> by <insert world organisation> to look for <insert mythological artifact or technological breakthrough>. However, <insert name of main character's oldest trusted friend> has other ideas and has sent <insert assasin with single physical perculiarity> to muck it all up. In the end though, the assasin is despatched and the hero returns home while his friend is exposed and probably killed.
No wonder DVC was a best seller, he'd had a few practice attempts beforehand...