It's actually quite different than the one I believe you have. It's 9 discs total. There are two discs for each movie and a bonus disc full of other junk. Here's the rundown:
Alien - The original theatrical cut, and the new extended director's cut that was just in theatres here a few months ago. I have yet to watch this extended version. I have my misgivings about whether it was necessary, but I'm definitely curious, as I am a big fan of the first movie. Plus there's a ton of bonus material.
Aliens - The original theatrical cut, and the extended edition. I remember years ago when the only way you could get the extended edition was on a special edition laser disc, now the theatrical cut is the one that's hard to find. It doesn't really matter though, the extended edition is far superior. Though completely different from the first movie, I still love it. Again, tons of bonus stuff.
Alien3 - This may sound strange, but this is one of the main reasons I bought this set. Ever since Alien3 came out, there have been rumors about how it was hacked up and that much longer better version that Fincher made was floating around. According to the liner notes, those rumors were exaggerated some, but there is still two versions here, the original and a brand new version (first time available) that's over a half hour longer. I watched it right away and I can say that I definitely enjoy it more.
Alien Resurrection - The director Jeunet says that he's happy with the theatrical cut, but for this edition, a second version with added scenes including a supposedly different ending (I have yet to watch it) is included. I think this movie is visually amazing and I can't wait to watch the extras on it.
Bottom line: I am a big fan of the Alien movies, and I think 70 bucks was well worth it considering the tons of shit you get in this box (8 movies, extras up the ass).