I like about 2/3 of Stephenson’s novels and Anathem took some work for me to get into. It really gets moving several hundred pages in and then the last 1/3 makes it all worth it.
It took me a few tries to get past the first 1/3rd of Anathem but once I did, it became one of my all time favorite books. Stephenson paints a rich rich world which I have often thought about outside of the major plot points of the book.
It's one of those books where you have no idea what's going on for the first chunk of the book--and probably don't really realize what's fully going on until close to the end. Reading a book in at least partial confusion can be taxing and hard to hold interest. (Though I certainly liked Anathem quite a bit overall.)