I believe all the blu-rays are the same as the already existing blu-ray releases (I can't be sure since I only had the old DVD release, but that's what I've read), with all the trimmings they already had. And they've just added this extra "Decoding Die Hard" disc - which is admittedly pretty great - to the bundle.
"Decoding Die Hard" covers all the movies, and features interviews with just about everyone who ever had anything to do with the series...except, strangely, Willis himself. And including, even more strangely, the creator of Chuck, lol. I mean, I know Reginald Veljohnson reprised his role as Al Powell in Chuck, but they don't mention that at all, so Chris Fedak's inclusion here seems like that of a totally random fan, haha.
Another bit of nice trivia that I didn't know, was that they got the title from Joel Silver's good friend, Shane Black, who was brainstorming titles for The Last Boyscout at the time.