This is a very good guide in terms of breaking down what you need for the various rankings and the location of the Memory Capsules. If you're only interested in completing the main game this is the book for you. However, I was a bit disappointed to see that it doesn't really discuss the Extra Missions. It tells you what they are and what you need to do to unlock them, but zero specifics. While some of the missions are pretty easy and need no explanation, others can present real challenges (especially for those of us who normally play mainly RPGs, not shooters); they're certainly harder than the game's normal mode.