I just finished up Anathem, by Neal Stephenson. This was a first-time read. I had fun reading it, and will read it again, but I wouldn't recommend it to absolutely everybody.
This is a typical Stephenson piece in many ways, and the author mentions the fun he had in building a consistent vocabulary for the world in the introduction. The paperback, with glossary and various addenda, comes up just short of 1000 pages. There would be footnotes citing the real science and philosophy that he used to build things, except this is a work of fiction and those don't have footnotes, and it would throw the reader out of the fictional world.
It is an alternate universe adventure, about a world where most of the world's philosophers, mathematicians, and scientists have settled themselves in enclaves roughly similar to cloistered monasteries. Fraa Erasmus, an Avout about twenty years old, last had contact with the Saecular world when he was about 10. His first Apert (the 10 days between periods of cloister the Avout have contact with the outside world) is coming up, he'd like to see his family again, he's trying to figure out girls (but not with much success, given that the suur he has a thing for is interested in somebody else), and what in the universe could possibly cause them to close the Starhenge for so long? Erasmus never intended to be an action hero saving the world, but he just might have to turn into one. (I mentioned the *alternate universe* part, right?)
Erasmus is a typical Stephenson hero: fantastically smart, but surrounded by people who are smarter and more driven than he is, and often seems to be pushed around by circumstances. Occasionally he struggles to captain his own fate, but ultimately gives in to the tide of the world (and the plot). Erasmus compares favorably to Daniel Waterhouse (from Stephenson's Baroque Cycle) and Lawrence Waterhouse (Cryptonomicon) despite having what I felt was nearly interchangeable personalities, because Erasmus is well-suited to this original universe rather than being an uncomfortably jammed in observer for the narrative to follow, brushing shoulders with the influential scientists of the day but stepping as lightly as a time-traveler so as not to change history. (If your only prior experience with Neal Stephenson is Snow Crash or Zodiac, both Hiro and Sangamon Taylor are more effective and driven than seems typical for the rest. They still don't quite know what to make of women despite being interested in them, though.)
Also in typical Stephenson style, there are lengthy bits where the characters get into philosophy, science, and math. Some of the lengthy asides have been summarized and stuffed into the back where you can read them or skip them at your pleasure. If you like Dan Brown but wish his books were longer and a bit more intellectual, you might like this. If you like the idea of ancient secrets, and philosophers and monks being kickass action heroes, but hate Dan Brown because his characters have occasionally had their brains replaced with sacks of gravel and the books encourage the conspiracy theorists, you might also like this.
: Except for when it's written by Terry Pratchett, who can get away with it because he's Terry Pratchett and knows how to make them work. Neal Stephenson recognizes that he's not Terry Pratchett and doesn't even try.