What I found most fascinating was that most of the boot camp experience is about inculcating the new recruits into the Marine culture. They have a longer cycle than, say, the Army's boot camp, but they get quite a bit less combat training and etc. Most of the focus is on instilling the values and morals the Marines find important. Speaking about the new recruits, Ricks writes:

Parris Island is the first place many of them ever encounter absolute and impersonal standards of right and wrong, of success and failure, says Sergeant Pabon, a native of Puerto Rico who learned to speak English at boot camp. "When they mess up at home, they don't get punished, they get 'explained.' The parents, the media, want to 'explain' everything. Here, you screw up, we stop you and penalize you immediately, before you forget it."

I've read several history books about different exploits of the Marines in battle, but never anything about how they became the way they were. This book offered great insight into their culture and mentality.