It certainly is something to watch with the whole family. I'm going to try to get my kids to watch it with me tonight (I have it on DVR; the Box Set pictured is available on July 24, 2008.)
The "secret" footage isn't actually very secret. Anyone can watch it, and people have for many years. Some of the footage is just rarely seen.
However, even though this footage is new or "secret", it looks a heck of a lot better: Discovery Channel was granted access to NASA's footage and remastered it all digitally and converted it to HD. In turn, they gave the footage back to NASA for future generations to enjoy.
This is a must watch that anyone can enjoy!