Well, it's Star Wars, and it's on Blu-ray, so you know there's no way it's not going to look and sound great. As everyone knows, George Lucas is a bit particular when it comes to the technical stuff, so prepare ye to use the Complete Saga box set to really show off that home theater system of yours.
All six films sport a brand-new 6.1 mix, which means the room is really going to shake from the bass when the Rancor lets out his angry roar in Return of the Jedi and it will seem like you're surrounded every time the TIE-fighters "Ehhhhhhhhh..." by.
However, the specifics -- and the limitations -- of the video transfer deserve mentioning. Except for The Phantom Menace, none of the films feature a brand-new HD transfer -- the films will be in high-def, but they're taken from the same transfer used for the 2004 DVDs. This is but a minor quibble and really more of a footnote, if anything -- the Star Wars films will still look the best they've ever looked, ever, and we'll probably get brand-new HD transfer in another box set somewhere down the line, anyway.