Fascinating if you're willing to take it on.
Anathem is an extremely ambitious book, but it is engrossing all the way through. The major premise is an earth-like world in which philosopher-scientist-monks segregate themselves from the rest of society in 'maths', opening their gates only every one, ten, hundred, or thousand years. A series of events, seen from the perspective of the endearing, honest, and occasionally sarcastic Fraa Erasmas, is gradually revealed to be larger and larger in scale. The result is world-altering.
The plot is overall pretty gripping; definitely not predictable. The sheer amount of new vocabulary introduced in the book can be confusing (especially with multiple names for similar things, or different names for the same thing at different points in the book), but the glossary helps to some extent.
You don't have to be intellectual or well-educated to read this book, but you do have to be curious; otherwise the various tangents will probably bore you. If you're willing to suspend your disbelief during expository dialogue, you can better appreciate the very intriguing concepts grappled with in the story.
Stephenson's satire is present throughout the novel, and is occasionally sharp-edged, especially towards religion. He doesn't condemn faith in the end, but it's certainly not treated gently.
Anathem completely held my attention, despite its length of well over 900 pages. The world is intriguing and detailed, the characters are compelling, the adventures are exciting, and characteristically, Stephenson's plot verges on mind-boggling. Overall, it works, and does so spectacularly.