I too got caught up in the frenzy surrounding The Da Vinci Code — I read it last spring and loved it, especially that it had very short chapters.
(It should come as no surprise that the Code has already been optioned to Hollywood.)
The mystery forming the framework of Code was familiar to me. Not only have I played Gabriel Knight: Blood of the Sacred, Blood of the Damned, I have read The Holy Blood and the Holy Grail (Michael Baigent, Richard Leigh, Henry Lincoln), which Brown references within the novel.
I had to read the previous adventure of Brown's hero, the Harvard symbologist.
Angels & Demons is not quite as friendly a beast. (But friendlier by far than Foucault's Pendulum.) For starters, I know little about the Illuminati, so the plot was much harder to swallow. I couldn't understand the motivation of most of the characters. I am unable to accept, let alone fathom, one of the book's central relationships — that between genius scientist Vittoria and her adopted father, the book's first victim, who is both a CERN scientist and a Catholic priest. I don't think it's common for priests to adopt children, and there are two such relationships in the novel. This is a weak ploy for building an emotional familial connection between characters.
Angels & Demons did, however, brilliantly paint Vatican City, secret passageways, ancient churches. It humanized the mystery of the papal conclave. The Vatican and its popes is rife with intrigue and conspiracy, with endless fodder for fiction. Having read about the "murder" of Pope John Paul I, perhaps I was able to suspend some components of disbelief quite readily.
Apparently there is more in store for our crime fighter, though I suspect the need for an expert in religious symbols may be limited. (I'd love to see a mystery based on the cult of the Black Madonna!) Although, there is a whole world of religion beyond Western Christianity to explore...