The POV of the second book jumps around a bit, actually, between Jane and a new character. Once you've finished eating the second book, you might want to find a copy of The Sagan Diaries before you go to the third.

I read Old Man's War in 2006. It may have been before I started my contract at Tektronix. The last three chapters had some incredibly powerful concepts and images that I needed to know at that precise time.