It's not a game. You know that, right? Good.
For Metal Gear fanatics, Digital Graphic Novel is a must, containing countless (unlockable) tidbits of data that are used to piece together the Shadow Moses Incident. But if 'Shadow Moses' doesn't ring a bell, then you're better off waiting for Portable Ops to get your Metal Gear fix on PSP -- unless you're a sucker for graphic novels.