I'm in the middle of that book now. It's dense, but other than that not a super difficult read (my 14 year-old daughter saw it on the coffee table and is reading it too now).
If you're wondering how it's 800 pages, the first 100 pages or so are about evidence for warfare in pre-agrarian society.
Bret's piece is about how this game somehow manages to reflect Gat's theory (and actual history).