Holy crap, a Heinlein book I liked... whodathunk?
I borrowed this because Michelle told me that it is a good counter-point to The Forever War, and I would have to agree.
This book is more military than sci-fi... in fact, it feels more military, using sci fi "bug" wars to cover boot camp, military life, officer's school and war. You could probably discuss the nuances and topics in this book for days, but at the same time enjoy it on a more shallow level.
It's very *FUCK YEAH!* propaganda, and serious, but a shit tonne of fun at the same time. Maybe it's my military family background that made me appreciate it more? I don't know, but it is one of the more enjoyable military-sci-fi-classic pieces out there, imo.