Well, as sad as it is that the actual "This Is It" show never happened, this is pretty much the best thing we can get, now. The documentary is very thorough in showing preparation, set design, and of course Jackson's health and mentality, and gives a pretty great idea of how incredible these shows would have been. The editing makes the best of the available footage, which isn't always of very good quality, but is always watchable and never impertinent.
There is one downside. A big part of watching this is to see how well MJ still performed days before his death. This being rehearsal footage, we never get to see him at his 100%: he always mentions that he is saving his voice and energy for the real shows. Despite this, no doubt is left that MJ was still quite on top of his game by the end of the movie. His rehearsal of Billy Jean in particular is incredible for a 50 year old: the fact remains that even at 60% effort, he remains an incredible showman.
In a sentence:
Tells you everything you can know about what MJ's This Is It show would have been like. Answer: incredible.
