Dead man dancing in “Michael Jackson’s This Is It,” and, boy, could he dance. The film, pieced together from 100 hours of rehearsal footage for his never-to-be concerts in London - concerts scheduled and contracted for before his untimely death last June - seems unfinished, and that is because it is unfinished: We will never see the show being rehearsed.

“This” really is his final curtain call. Jackson, a shockingly gaunt man with large hands and feet, a delicate head and a face that was both iconic and grotesque, speaks in that whispery, girlish voice, and yet commands attention, and when he sings and dances, which he does at half-speed most of the time, it is obvious he remained divinely gifted.

Director Kenny Ortega of “High School Musical” fame is a deferential, solicitous figure in the film as he “directs” the rehearsals, carefully making sure that “MJ” approves his every step. Ortega was more of an editor than director in regard to this film, which combines multiple rehearsals of many of Jackson’s best loved songs, seeking no doubt to find the cuts, some of them seemingly overdubbed, that have the most oomph.

By and large Ortega succeeds, and “This Is It” is a worthwhile concert film-cum-memorial to Jackson, who had such a profound impact on young fans across the world, even if the film is finally not entirely up to the artists’s own standards.

We see too much hero worship by trembling young dancers and singers, one too many shots of Jackson’s bony hand on his bony pelvis, and one sequence indulges Jackson’s penchant for messianic narcissism, one of his least likable traits.

But “This Is It” also lets us see how Jackson, a major artist not far off his game, prepared for a performance, his improvised bits of song and dance and throwaway lines.

As a dancer, he was a pop Nijinsky, an equal to Fred Astaire and Gene Kelly, whom he idolized, and “This Is It” gives fans of his dancing ample pleasure. Again, even at half-speed, and at times almost standing still, he is amazing to watch.

One memorable sequence restages the “Thriller” music video originally directed by John Landis. Jackson was never a feature-film star. He was just too strange. But Landis (“The Blues Brothers,” etc.) proved, and this film reminds us, that in a music video Jackson was the biggest star in the world.

(”Michael Jackson’s This Is It” contains suggestive choreography and scary images)

Rated PG. At the AMC Boston Common, Regal Fenway 13 and suburban theaters.