Michael Jackson always said that he wished he could live on stage, and in Michael Jackson’s This Is It, there isn’t a moment when he looks less than comfortably and pleasurably at home there. On the vast, half-empty, often darkened proscenium of the Staples Center in Los Angeles, where we see him in bare-bones videotaped rehearsals for the 50 London concerts that he never lived to perform, Jackson moves lightly and easily, with his herky-jerky demon-marionette grace. On the rare occasions when he’s not focused on dance moves and has nothing to do but sing, as in a soaring interlude of ”Human Nature” or a version of ”I Want You Back” that he tosses off with affection for his child-superstar pluck, the music pours out of him like sunlight.

This Is It is not in any way ghoulish. It has now been established that when Jackson died, he was, physically speaking, a relatively healthy man. And so we’re spared the macabre spectacle of combing the movie for any literal signs that he was knocking at death’s door. It should also be said, though, that in This Is It, Jackson shows no telltale signs of a broken spirit, either. From the moment he takes the stage, he’s loose, robust, and in control. Maybe a little too in control. In the relative privacy of these rehearsal sessions, which took place from March of this year until his death on June 25, Jackson comes off as his friends have often described him — as a gentle, sweet, but very shrewd soul who was also a painful perfectionist. Coaching his keyboardist and musical director, Michael Bearden, on how to play ”The Way You Make Me Feel” with the exact right syncopated pull, Jackson says that he wants the song to sound ”like you’re dragging yourself out of bed,” but Bearden can’t seem to get it. Though they banter a bit about the word ”booty,” we get a hint of what a frosty taskmaster Jackson could be. When he’s displeased, it stings.

As the last set of images we’ll ever have of Michael Jackson, This Is It offers a raw and endearing sketch of a genius at work. The movie was directed, by Kenny Ortega, with enough liveliness to make up for its home-movie scruffiness, and I had a good time reveling in what amounts to a soft-edged vérité scrapbook for Michael-maniacs. By the end, though, This Is It feels like the half-complete experience that it is — a mere diagram of the excitement that Michael, for his comeback, had planned to unleash upon the world.

It’s clear from the movie that the London concerts were conceived as a very grand series of onstage music videos, each with a huge, intricate set that at times involved digital projections, and each choreographed as a disco-inferno Broadway showstopper. (”Thriller,” one of the few songs we watch as it was meant to be, had a full earth-packed graveyard.) The dancers were going to pop out from beneath the stage and crawl over skyscrapers, as Michael shimmied and boogied and got lifted into the air. Watching this without most of the sets, with the gears and pulleys still showing, and from two functional camera angles in front of the stage, we get the flavor of the songs but not the majesty.

And that’s not just due to the lack of trappings. Jackson, it’s clear, held back in rehearsal. In This Is It, he’s singing and dancing, but he’s also watching himself sing and dance, stepping out of his performance. What’s missing — what the film gives you only a tantalizing glimpse of — is his ferocity. When he does a tamped-down version of his solo whirligig in ”Billie Jean,” playing air guitar on his crotch (a gesture that elicits a round of cheers from the dancers in the Staples Center), you feel him sketching in the heat without quite committing himself. ”At least we get a feel of it,” he says.

This Is It is fun, but it’s a slightly airless experience. If the movie allows you to bask in Michael Jackson’s aura, it also uses his image to foster ”nostalgia” for a concert epiphany that never quite was. Maybe it was Michael’s destiny to leave us all wanting more. Would those concerts have returned him to his magical pedestal? We’ll never know the answer, of course. But watching this movie, at least we get a feel of it