It's hard to encapsulate a book that is so large in scope and so enjoyable to read. Your intellect revolts at trying to peg it down by mere description and emotionally... well... I just didn't want the thing to end. When I found, on his site, someone had actually been inspired enough to create music (http://nealstephenson.com/anathem/music....) for Anathem I was amazed but, now that I'm done, I understand.
What can I say that you can't read elsewhere. I might warn you that Stephenson is a master world builder and so it takes effort to get out of this world and into his. But, by God, it's worth the effort!