Neal Stephenson must be one of the most intelligent men on the planet: knowledgeable on philosophy, mathematics, science, computers, history - and that's the problem with his books, you feel like you are being overwhelmed, and you need to take evening classes to understand them.
I have read the whole Baraque cycle, Anathem, Diamond Age and Cryptonomicum. Love them all, but want to sit down and reread them with a friend who is an expert on mathematics, one on science, one on computers, and one on philosophy. I'll bring a decent historical knowledge to the table, and just teach each other and discuss all the different aspects of his novels.
I would prob recommend Diamond Age as his most accessible - and Anathem as his toughest. Definitely worth reading at least one or two by him at some point in your life though - just be prepared to read slowly and have a lot of questions!