By unexplored, I mean elements that were not established previously or just came out of the blue. Off the top of my head: The Trade Federation (Who are they and why should we care about them?) Sifo-Dyas (Master...who? Was he ever in Episode I?) The Clone Army (Precursors to Stormtroopers? Cool, but when did this happen? Where was this in Episode I?) Count Dooku (How and when did Sidious get Dracula to be his apprentice?) General Grevious (Wait, this guy was in a cartoon? I thought only the movies counted!) The so-called "Tragedy" of Darth Plagueis the Wise (Darth...who? Was he ever in Episode I and II?) Looking back, the way George wrote the prequels was as if he knew that Expanded Universe stuff was out there and just figured that any who want to know more can just look at that. Which, for the hardcore Star Wars fan, is well and good, but for the general, casual fan, they'd be lost. I've talked with people about this, and a few say that as one of the flaws of the prequels. A certain internet reviewer that talks about comic books also said as much, that if you require supplementary material to watch your movie, then you've failed as a filmmaker.