This review will be shorter than most due to the nature of the film.
This Is It is not about Michael Jackson. It is not about his life, it is not about his death, though it does provide details about him as a person. At very least, one aspect of him - his level of commitment to his art.
This Is It follows the making-of process of what was to be Michael Jackson's ultimate concert. That's pretty much all you need to know. As you'd expect from a Michael Jackson performance, it is a treat to watch and listen to.
Plenty of behind-the-scenes footage is shown: choreography, makeup/costumes, special effects, lighting, etc. You really get a sense of how much of a perfectionist Michael Jackson was in terms of his music. The film features some of his all-time classics (I won't name any songs to prevent spoilers) and to see them come to life in such wonderful, strange, and unexpected ways was nothing short of amazing.
If you are a fan of Michael Jackson, you really need to see This Is It. And stay for the credits. The extra little bonuses at the end of the credits are worth it. One of them in particular made me day.