It may start slow (though personally I loved the start), but it sure picks up towards the last third. It blew my mind into many, many pieces.
I'd give a strong recommendation to stick with it - at first all of the strange invented terms are a bit jarring but after a while they become natural and you get to enjoy what I would regard as one of the finest work of fiction of recent years.
shudder
I've liked some Neal Stephenson, and I wanted to like Anathem, but just could not get "into" it. Maybe I'll have to try it again.
kb