I totally agree - after reading DaVinci Code and Digital Fortress, I can pretty much sum up Dan Brown's formula as the following:

- Start off with an interesting hook and quickly diverge into two (or more) concurrent plots. Minimal character development is necessary.
- Devote alternating chapters to each plot
- End each (short) chapter with a 'cliffhanger' style situation. This gives the 'page-turner' feel because there's always some unresolved situation that haunts you during reading.
- Don't worry about factual accuracy. Better yet, ignore accuracy altogether if it hampers the plot.
- Make the two concurrent plots collide during the last chapter or two of the book and tidy up the situation entirely too neatly.

It's not that either of the books is a bad read - I've read much worse... it's just the formulaic predictability that makes me want to stay away from anything else he might churn out :(