This is a decent documentary as it gives you some insight into the making of this famous special. From a music and TV historian's point of view, you get a laugh out of the concepts and costumes, and what was considered risqué at the time. Elvis looks great (in fact, probably the best he ever looked), and you get a taste of all his music.
The negative: it would've been much better to not have known that Steve Binder was an executive producer on this show. He made sure to have many of the participants praise him up one side and down the other. It was a little gratuitous by the end. Yes, we understood that you did everything right, and Elvis trusted you more than anyone else in the room. And yes, Colonel Parker was "the devil/monster" (probably all true, but a little humility goes a long way).
Positive: if you're an Elvis fan, you will find a lot of enjoyment in it and get some backstage secrets. Unless you have no idea who Elvis is, you will still get a better idea of who the man really was.