2XS, Burning Bright, Worlds Without End, and Psychotrope. Chips, Bugs, Immortal Elves, and AI/Otaku - they're what's for breakfast. That should give you essential background (not, Opti, that I think you really need it at this point), but then you can move onto the new stuff.
Really, the new stuff is where it's at - though I should point out that AFAIK, the only critical must-reads are the Fear The Dark fiction, as much of that hasn't made it into the game books yet. Otherwise all the true metaplot stuff is found primarily, if not exclusively, in the game books.